Report PreloadingTriggeringOutcome to UMA.

A new histogram "Preloading.{PreloadingType}.Attempt
{PreloadingPredictor}.TriggeringOutcome" is added to track the terminal
status of preloading events, for which we can derive the number of
prefetches, prefetches success rate etc.

PreloadingPredictor is changed from enum class to a normal class so that
it holds both the UKM enum as well as the string description. With such,
- ContentPreloadingPredictor / ChromePreloadingPredictor are removed,
  along with all the associated ToPreloadingPredictor cast methods.
- {Chrome|Content}PreloadingPredictor::PredictorXYZ is re-expressed
  with {chrome|content}_preloading_predictor::PredictorXYZ namespace.
- PreloadingPredictor content layer enum boundaries are removed. The
  enum validity check is placed into PreloadingDataImpl, just before
  the predictions and attempts are reported to UKM.


Note: the triggering outcome metrics can be derived from the Precog UKMs
but a UMA histogram can answer them much more directly.

Bug: 1406238
Change-Id: If1742b1e3a0cf2803c614d2c4c7d0cbe610057ec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4149348
Reviewed-by: Sreeja Kamishetty <sreejakshetty@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Simon Pelchat <spelchat@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: William Liu <liuwilliam@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1095788}

chrome/browser/navigation_predictor/anchor_element_preloader.cc

@@ -51,10 +51,10 @@ void AnchorElementPreloader::MaybePreconnect(const GURL& target) {
   // likely compute the confidence by looking at different factors (e.g. anchor
   // element dimensions, last time since scroll, etc.).
   preloading_data->AddPreloadingPrediction(
-      ToPreloadingPredictor(ChromePreloadingPredictor::kPointerDownOnAnchor),
+      chrome_preloading_predictor::kPointerDownOnAnchor,
       /*confidence=*/100, match_callback);
   content::PreloadingAttempt* attempt = preloading_data->AddPreloadingAttempt(
-      ToPreloadingPredictor(ChromePreloadingPredictor::kPointerDownOnAnchor),
+      chrome_preloading_predictor::kPointerDownOnAnchor,
       content::PreloadingType::kPreconnect, match_callback);
 
   if (content::PreloadingEligibility eligibility =

chrome/browser/navigation_predictor/anchor_element_preloader_browsertest.cc

@@ -71,8 +71,7 @@ class AnchorElementPreloaderBrowserTest
     test_ukm_recorder_ = std::make_unique<ukm::TestAutoSetUkmRecorder>();
     ukm_entry_builder_ =
         std::make_unique<content::test::PreloadingAttemptUkmEntryBuilder>(
-            ToPreloadingPredictor(
-                ChromePreloadingPredictor::kPointerDownOnAnchor));
+            chrome_preloading_predictor::kPointerDownOnAnchor);
     test_timer_ = std::make_unique<base::ScopedMockElapsedTimersForTest>();
     ASSERT_TRUE(loading_predictor);
     loading_predictor->preconnect_manager()->SetObserverForTesting(this);

chrome/browser/predictors/autocomplete_action_predictor.cc

@@ -212,8 +212,7 @@ void AutocompleteActionPredictor::StartPrerendering(
     // this prerendering attempt for Prerender.
     content::PreloadingAttempt* preloading_attempt =
         preloading_data->AddPreloadingAttempt(
-            ToPreloadingPredictor(
-                ChromePreloadingPredictor::kOmniboxDirectURLInput),
+            chrome_preloading_predictor::kOmniboxDirectURLInput,
             content::PreloadingType::kPrerender, std::move(same_url_matcher));
 
     PrerenderManager::CreateForWebContents(&web_contents);
@@ -227,8 +226,7 @@ void AutocompleteActionPredictor::StartPrerendering(
     // this preloading attempt for NoStatePrefetch.
     content::PreloadingAttempt* preloading_attempt =
         preloading_data->AddPreloadingAttempt(
-            ToPreloadingPredictor(
-                ChromePreloadingPredictor::kOmniboxDirectURLInput),
+            chrome_preloading_predictor::kOmniboxDirectURLInput,
             content::PreloadingType::kNoStatePrefetch,
             std::move(same_url_matcher));
 
@@ -318,8 +316,7 @@ AutocompleteActionPredictor::RecommendAction(
     // We multiply confidence by 100 to pass the percentage and cast it into int
     // for logs.
     preloading_data->AddPreloadingPrediction(
-        ToPreloadingPredictor(
-            ChromePreloadingPredictor::kOmniboxDirectURLInput),
+        chrome_preloading_predictor::kOmniboxDirectURLInput,
         static_cast<int64_t>(confidence * 100), std::move(same_url_matcher));
   }
 

chrome/browser/predictors/autocomplete_action_predictor_unittest.cc

@@ -123,8 +123,7 @@ class AutocompleteActionPredictorTest : public testing::Test {
         profile_.get(), nullptr);
     ukm_entry_builder_ =
         std::make_unique<content::test::PreloadingPredictionUkmEntryBuilder>(
-            ToPreloadingPredictor(
-                ChromePreloadingPredictor::kOmniboxDirectURLInput));
+            chrome_preloading_predictor::kOmniboxDirectURLInput);
     test_ukm_recorder_ = std::make_unique<ukm::TestAutoSetUkmRecorder>();
     test_timer_ = std::make_unique<base::ScopedMockElapsedTimersForTest>();
 

chrome/browser/preloading/chrome_preloading.cc

@@ -3,15 +3,14 @@
 // found in the LICENSE file.
 
 #include "chrome/browser/preloading/chrome_preloading.h"
+
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/search_engines/template_url_service_factory.h"
 #include "components/search_engines/template_url.h"
 #include "components/search_engines/template_url_service.h"
 #include "content/public/browser/browser_context.h"
 #include "url/gurl.h"
 
-using content::PreloadingPredictor;
-
 namespace {
 
 bool IsSideSearch(content::BrowserContext* browser_context, const GURL& url) {
@@ -31,11 +30,6 @@ bool IsSideSearch(content::BrowserContext* browser_context, const GURL& url) {
 
 }  // namespace
 
-content::PreloadingPredictor ToPreloadingPredictor(
-    ChromePreloadingPredictor predictor) {
-  return static_cast<content::PreloadingPredictor>(predictor);
-}
-
 content::PreloadingEligibility ToPreloadingEligibility(
     ChromePreloadingEligibility eligibility) {
   return static_cast<content::PreloadingEligibility>(eligibility);

chrome/browser/preloading/chrome_preloading.h

@@ -13,63 +13,66 @@
 #include "url/gurl.h"
 
 class TemplateURLService;
-using content::PreloadingPredictor;
 
-// If you change any of the following emums, please follow the process in
-// go/preloading-dashboard-updates to update the mapping reflected in
-// dashboard, or if you are not a Googler, please file an FYI bug on
-// https://crbug.new with component Internals>Preload.
+// If you change any of the following enums or static variables, please follow
+// the process in go/preloading-dashboard-updates to update the mapping
+// reflected in dashboard, or if you are not a Googler, please file an FYI bug
+// on https://crbug.new with component Internals>Preload.
 
 // Defines various embedder triggering mechanisms which triggers different
 // preloading operations mentioned in //content/public/browser/preloading.h.
 
 // These values are persisted to logs. Entries should not be renumbered and
 // numeric values should never be reused.
-enum class ChromePreloadingPredictor {
-  // Numbering starts from `kPreloadingPredictorContentEnd` defined in
-  // //content/browser/public/preloading.h . Advance numbering by +1 when adding
-  // a new element.
-
-  // When the preloading URL is predicted from the Omnibox Direct URL Input
-  // (DUI). This is used to perform various preloading operations like prefetch
-  // and prerender to load Omnibox predicted URLs faster.
-  kOmniboxDirectURLInput =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd),
-
-  // When a pointerdown (e.g. mousedown or touchstart) event happens on an
-  // anchor element with an href value pointing to an HTTP(S) origin, we may
-  // attempt to preload the link.
-  kPointerDownOnAnchor =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd) + 1,
-
-  // When the preloading URL is predicted from the default search suggest
-  // service for faster search page loads.
-  kDefaultSearchEngine =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd) + 2,
-
-  // When the preloading URL is predicted from the default search suggest due to
-  // change in Omnibox selection.
-  kOmniboxSearchPredictor =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd) + 3,
-
-  // When the preloading URL is predicted from the default search suggest due to
-  // mouse being pressed down on a Omnibox Search suggestion.
-  kOmniboxMousePredictor =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd) + 4,
-
-  // When the default match in omnibox has the search prefetch or prerender
-  // hint.
-  kOmniboxSearchSuggestDefaultMatch =
-      static_cast<int>(PreloadingPredictor::kPreloadingPredictorContentEnd) + 5,
-
-  // TODO(crbug.com/1309934): Integrate more Preloading predictors with
-  // Preloading logging APIs.
-};
-
-// Helper method to convert ChromePreloadingPredictor to
-// content::PreloadingPredictor to avoid casting.
-content::PreloadingPredictor ToPreloadingPredictor(
-    ChromePreloadingPredictor predictor);
+//
+// Advance numbering by +1 when adding a new element.
+//
+// Please make sure Chrome `PreloadingPredictor` are defined after 100
+// (inclusive) as 99 and below are reserved for content-public and
+// content-internal definitions. Both the value and the name should be unique
+// across all the namespaces.
+namespace chrome_preloading_predictor {
+// When the preloading URL is predicted from the Omnibox Direct URL Input
+// (DUI). This is used to perform various preloading operations like prefetch
+// and prerender to load Omnibox predicted URLs faster.
+static constexpr content::PreloadingPredictor kOmniboxDirectURLInput(
+    100,
+    "OmniboxDirectURLInput");
+
+// When a pointerdown (e.g. mousedown or touchstart) event happens on an
+// anchor element with an href value pointing to an HTTP(S) origin, we may
+// attempt to preload the link.
+static constexpr content::PreloadingPredictor kPointerDownOnAnchor(
+    101,
+    "PointerDownOnAnchor");
+
+// When the preloading URL is predicted from the default search suggest
+// service for faster search page loads.
+static constexpr content::PreloadingPredictor kDefaultSearchEngine(
+    102,
+    "DefaultSearchEngine");
+
+// When the preloading URL is predicted from the default search suggest due to
+// change in Omnibox selection.
+static constexpr content::PreloadingPredictor kOmniboxSearchPredictor(
+    103,
+    "OmniboxSearchPredictor");
+
+// When the preloading URL is predicted from the default search suggest due to
+// mouse being pressed down on a Omnibox Search suggestion.
+static constexpr content::PreloadingPredictor kOmniboxMousePredictor(
+    104,
+    "OmniboxMousePredictor");
+
+// When the default match in omnibox has the search prefetch or prerender
+// hint.
+static constexpr content::PreloadingPredictor kOmniboxSearchSuggestDefaultMatch(
+    105,
+    "OmniboxSearchSuggestDefaultMatch");
+
+// TODO(crbug.com/1309934): Integrate more Preloading predictors with
+// Preloading logging APIs.
+}  // namespace chrome_preloading_predictor
 
 // These values are persisted to logs. Entries should not be renumbered and
 // numeric values should never be reused.

chrome/browser/preloading/prefetch/no_state_prefetch/prerender_nostate_prefetch_browsertest.cc

@@ -305,11 +305,10 @@ class NoStatePrefetchBrowserTest
     test_ukm_recorder_ = std::make_unique<ukm::TestAutoSetUkmRecorder>();
     omnibox_attempt_entry_builder_ =
         std::make_unique<content::test::PreloadingAttemptUkmEntryBuilder>(
-            ToPreloadingPredictor(
-                ChromePreloadingPredictor::kOmniboxDirectURLInput));
+            chrome_preloading_predictor::kOmniboxDirectURLInput);
     link_rel_attempt_entry_builder_ =
         std::make_unique<content::test::PreloadingAttemptUkmEntryBuilder>(
-            content::PreloadingPredictor::kLinkRel);
+            content::preloading_predictor::kLinkRel);
     test_timer_ = std::make_unique<base::ScopedMockElapsedTimersForTest>();
     host_resolver()->AddRule("*", "127.0.0.1");
   }

chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_browser_test_base.cc

@@ -10,6 +10,7 @@
 #include "base/task/single_thread_task_runner.h"
 #include "chrome/browser/devtools/devtools_window.h"
 #include "chrome/browser/devtools/devtools_window_testing.h"
+#include "chrome/browser/preloading/chrome_preloading.h"
 #include "chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_request.h"
 #include "chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_service.h"
 #include "chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_service_factory.h"

chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_service.cc

@@ -197,14 +197,14 @@ bool SearchPrefetchService::MaybePrefetchURL(
     const GURL& url,
     content::WebContents* web_contents) {
   return MaybePrefetchURL(url, /*navigation_prefetch=*/false, web_contents,
-                          ChromePreloadingPredictor::kDefaultSearchEngine);
+                          chrome_preloading_predictor::kDefaultSearchEngine);
 }
 
 bool SearchPrefetchService::MaybePrefetchURL(
     const GURL& url,
     bool navigation_prefetch,
     content::WebContents* web_contents,
-    ChromePreloadingPredictor predictor) {
+    content::PreloadingPredictor predictor) {
   if (!SearchPrefetchServicePrefetchingIsEnabled())
     return false;
 
@@ -242,8 +242,7 @@ bool SearchPrefetchService::MaybePrefetchURL(
   // this DefaultSearchEngine or OmniboxSearchPredictor prefetch attempt when
   // |navigation_prefetch| is true.
   attempt = preloading_data->AddPreloadingAttempt(
-      ToPreloadingPredictor(predictor), content::PreloadingType::kPrefetch,
-      same_url_matcher);
+      predictor, content::PreloadingType::kPrefetch, same_url_matcher);
 
   if (!search_with_terms) {
     recorder.reason_ =
@@ -648,8 +647,8 @@ void SearchPrefetchService::OnResultChanged(content::WebContents* web_contents,
 
     // Create PreloadingPrediction for this match.
     preloading_data->AddPreloadingPrediction(
-        ToPreloadingPredictor(ChromePreloadingPredictor::kDefaultSearchEngine),
-        confidence, std::move(same_url_matcher));
+        chrome_preloading_predictor::kDefaultSearchEngine, confidence,
+        std::move(same_url_matcher));
 
     // Record a prediction for default match prefetch suggest predictions.
     if (result.default_match() == &match) {
@@ -662,8 +661,7 @@ void SearchPrefetchService::OnResultChanged(content::WebContents* web_contents,
 
       // Create PreloadingPrediction for this match.
       preloading_data->AddPreloadingPrediction(
-          ToPreloadingPredictor(
-              ChromePreloadingPredictor::kOmniboxSearchSuggestDefaultMatch),
+          chrome_preloading_predictor::kOmniboxSearchSuggestDefaultMatch,
           confidence, std::move(same_url_matcher));
     } else if (OnlyAllowDefaultMatchPreloading()) {
       // Only prefetch default match when in the experiment.
@@ -781,17 +779,17 @@ void SearchPrefetchService::OnNavigationLikely(
       [](NavigationPredictor navigation_predictor) {
         switch (navigation_predictor) {
           case NavigationPredictor::kMouseDown:
-            return ChromePreloadingPredictor::kOmniboxMousePredictor;
+            return chrome_preloading_predictor::kOmniboxMousePredictor;
           case NavigationPredictor::kUpOrDownArrowButton:
-            return ChromePreloadingPredictor::kOmniboxSearchPredictor;
+            return chrome_preloading_predictor::kOmniboxSearchPredictor;
         }
       };
   auto predictor = navigation_likely_event_to_predictor(navigation_predictor);
 
   // Create PreloadingPrediction for this match. We set the confidence to 100 as
   // when the user changed the selected match, we always trigger prefetch.
-  preloading_data->AddPreloadingPrediction(ToPreloadingPredictor(predictor),
-                                           100, std::move(same_url_matcher));
+  preloading_data->AddPreloadingPrediction(predictor, 100,
+                                           std::move(same_url_matcher));
   MaybePrefetchURL(preload_url,
                    /*navigation_prefetch=*/true, web_contents, predictor);
 }
@@ -998,8 +996,7 @@ void SearchPrefetchService::CoordinatePrefetchWithPrerender(
       content::PreloadingData::GetOrCreateForWebContents(web_contents);
   content::PreloadingAttempt* preloading_attempt =
       preloading_data->AddPreloadingAttempt(
-          ToPreloadingPredictor(
-              ChromePreloadingPredictor::kDefaultSearchEngine),
+          chrome_preloading_predictor::kDefaultSearchEngine,
           content::PreloadingType::kPrerender, same_url_matcher);
 
   auto prefetch_request_iter = prefetches_.find(canonical_search_url);

chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_service.h

@@ -15,14 +15,14 @@
 #include "base/scoped_observation.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
-#include "chrome/browser/preloading/chrome_preloading.h"
 #include "chrome/browser/preloading/prefetch/search_prefetch/search_prefetch_request.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "components/omnibox/browser/autocomplete_match.h"
 #include "components/omnibox/browser/omnibox.mojom-shared.h"
 #include "components/search_engines/template_url_data.h"
 #include "components/search_engines/template_url_service.h"
 #include "components/search_engines/template_url_service_observer.h"
+#include "content/public/browser/preloading.h"
 #include "third_party/abseil-cpp/absl/types/optional.h"
 #include "url/gurl.h"
 
@@ -211,7 +211,7 @@ class SearchPrefetchService : public KeyedService,
   bool MaybePrefetchURL(const GURL& url,
                         bool navigation_prefetch,
                         content::WebContents* web_contents,
-                        ChromePreloadingPredictor predictor);
+                        content::PreloadingPredictor predictor);
 
   // Adds |this| as an observer of |template_url_service| if not added already.
   void ObserveTemplateURLService(TemplateURLService* template_url_service);