preload: Add LINT.Change to check new prerender trigger types

This CL adds LINT.Change and a document link to prerender_utils.cc
about how to include the newly added prerender trigger types in metrics.

Bug: 1462832
Change-Id: I870bf8a4bddf8091410387b97ff42465b7b97343
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4795933
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Huanpo Lin <robertlin@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1188740}

chrome/browser/preloading/prerender/prerender_utils.cc

@@ -14,10 +14,15 @@ BASE_FEATURE(kHidePrefetchParameter,
              "HidePrefetchParameter",
              base::FEATURE_ENABLED_BY_DEFAULT);
 
+// If you add a new type of prerender trigger, please refer to the internal
+// document go/update-prerender-new-trigger-metrics to make sure that metrics
+// include the newly added trigger type.
+// LINT.IfChange
 const char kDefaultSearchEngineMetricSuffix[] = "DefaultSearchEngine";
 const char kDirectUrlInputMetricSuffix[] = "DirectURLInput";
 const char kBookmarkBarMetricSuffix[] = "BookmarkBar";
 const char kNewTabPageMetricSuffix[] = "NewTabPage";
+// LINT.ThenChange()
 
 bool IsDirectUrlInputPrerenderEnabled() {
   return base::FeatureList::IsEnabled(features::kOmniboxTriggerForPrerender2);

content/public/browser/prerender_trigger_type.h

@@ -7,6 +7,11 @@
 
 namespace content {
 
+// If you add a new type of prerender trigger, please refer to the internal
+// document go/update-prerender-new-trigger-metrics to make sure that metrics
+// include the newly added trigger type. The string for the trigger type is
+// generated in PrerenderPageLoadMetricsObserver::AppendSuffix.
+// LINT.IfChange
 enum class PrerenderTriggerType {
   // https://wicg.github.io/nav-speculation/prerendering.html#speculation-rules
   kSpeculationRule,
@@ -15,6 +20,7 @@ enum class PrerenderTriggerType {
   // Trigger used by content embedders.
   kEmbedder,
 };
+// LINT.ThenChange(//components/page_load_metrics/browser/observers/prerender_page_load_metrics_observer.cc)
 
 }  // namespace content