[bfcache] Launch BackForwardCacheEnabledForNonPluginEmbed

It's currently Stable 50% with the following metrics:

- Cache Hit: 28.86% => 29.15% (p-value: ◆◆◆◆)
- Blocklisted feature: ContainsPlugins 12.27% -> 0.97%

This CL removes the flag guarding this feature, and update `back_forward_cache_browsertest.cc` to use `kDummy` as blocklisted feature instead (as browser test in content/ cannot load pdf plugin)

Bug: 1325192
Change-Id: Ifcd97bf9be8d657a70fb7de2e5d201889394a0ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3925075
Commit-Queue: Ming-Ying Chung <mych@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1052811}

chrome/browser/chrome_back_forward_cache_browsertest.cc

@@ -678,13 +678,6 @@ class ChromeBackForwardCacheBrowserWithEmbedTest
   }
 
  protected:
-  void SetUpCommandLine(base::CommandLine* command_line) override {
-    // Allow BackForwardCache for non-plugin embedded elements.
-    EnableFeatureAndSetParams(
-        blink::features::kBackForwardCacheEnabledForNonPluginEmbed, "", "");
-    ChromeBackForwardCacheBrowserTest::SetUpCommandLine(command_line);
-  }
-
   void ExpectBlocklistedFeature(
       blink::scheduler::WebSchedulerTrackedFeature feature,
       base::Location location) {

content/browser/back_forward_cache_browsertest.cc

@@ -2502,19 +2502,17 @@ bool BackForwardCacheBrowserTest::IsUnloadAllowedToEnterBackForwardCache() {
 }
 
 bool BackForwardCacheBrowserTest::AddBlocklistedFeature(RenderFrameHost* rfh) {
-  return ExecJs(rfh, R"(
-    let object = document.createElement("object");
-    object.type = "application/x-blink-test-plugin";
-    document.body.appendChild(object);
-  )");
+  // Add kDummy as blocking feature.
+  RenderFrameHostImplWrapper rfh_a(rfh);
+  rfh_a->UseDummyStickyBackForwardCacheDisablingFeatureForTesting();
+  return true;
 }
 
 void BackForwardCacheBrowserTest::ExpectNotRestoredDueToBlocklistedFeature(
     base::Location location) {
-  ExpectNotRestored(
-      {NotRestoredReason::kBlocklistedFeatures},
-      {blink::scheduler::WebSchedulerTrackedFeature::kContainsPlugins}, {}, {},
-      {}, location);
+  ExpectNotRestored({NotRestoredReason::kBlocklistedFeatures},
+                    {blink::scheduler::WebSchedulerTrackedFeature::kDummy}, {},
+                    {}, {}, location);
 }
 
 const ukm::TestAutoSetUkmRecorder& BackForwardCacheBrowserTest::ukm_recorder() {

third_party/blink/common/features.cc

@@ -1301,10 +1301,6 @@ BASE_FEATURE(kBackForwardCacheAppBanner,
              "BackForwardCacheAppBanner",
              base::FEATURE_ENABLED_BY_DEFAULT);
 
-BASE_FEATURE(kBackForwardCacheEnabledForNonPluginEmbed,
-             "BackForwardCacheEnabledForNonPluginEmbed",
-             base::FEATURE_DISABLED_BY_DEFAULT);
-
 // Initialize CSSDefaultStyleSheets early in renderer startup.
 BASE_FEATURE(kDefaultStyleSheetsEarlyInit,
              "DefaultStyleSheetsEarlyInit",

third_party/blink/public/common/features.h

@@ -572,11 +572,6 @@ BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kPrefetchAndroidFonts);
 // back/forward cache.
 BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kBackForwardCacheAppBanner);
 
-// Enables back/forward cache for non-plugin embeds.
-// TODO(crbug.com/1325192): Remove once the bug is resolved.
-BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(
-    kBackForwardCacheEnabledForNonPluginEmbed);
-
 BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kDefaultStyleSheetsEarlyInit);
 
 BLINK_COMMON_EXPORT BASE_DECLARE_FEATURE(kSystemColorChooser);

third_party/blink/renderer/core/html/html_plugin_element.cc

@@ -126,14 +126,6 @@ HTMLPlugInElement::HTMLPlugInElement(const QualifiedName& tag_name,
       // simpler to make both classes share the same codepath in this class.
       needs_plugin_update_(!flags.IsCreatedByParser()) {
   SetHasCustomStyleCallbacks();
-  if (!base::FeatureList::IsEnabled(
-          features::kBackForwardCacheEnabledForNonPluginEmbed)) {
-    if (auto* context = doc.GetExecutionContext()) {
-      context->GetScheduler()->RegisterStickyFeature(
-          SchedulingPolicy::Feature::kContainsPlugins,
-          {SchedulingPolicy::DisableBackForwardCache()});
-    }
-  }
 }
 
 HTMLPlugInElement::~HTMLPlugInElement() {
@@ -697,16 +689,13 @@ bool HTMLPlugInElement::LoadPlugin(const KURL& url,
     layout_object->GetFrameView()->AddPlugin(plugin);
   }
 
-  if (base::FeatureList::IsEnabled(
-          features::kBackForwardCacheEnabledForNonPluginEmbed)) {
-    // Disable back/forward cache when a document uses a plugin. This is not
-    // done in the constructor since |HTMLPlugInElement| is a base class for
-    // HTMLObjectElement and HTMLEmbedElement which can host child browsing
-    // contexts instead.
-    GetExecutionContext()->GetScheduler()->RegisterStickyFeature(
-        SchedulingPolicy::Feature::kContainsPlugins,
-        {SchedulingPolicy::DisableBackForwardCache()});
-  }
+  // Disable back/forward cache when a document uses a plugin. This is not
+  // done in the constructor since `HTMLPlugInElement` is a base class for
+  // HTMLObjectElement and HTMLEmbedElement which can host child browsing
+  // contexts instead.
+  GetExecutionContext()->GetScheduler()->RegisterStickyFeature(
+      SchedulingPolicy::Feature::kContainsPlugins,
+      {SchedulingPolicy::DisableBackForwardCache()});
 
   GetDocument().SetContainsPlugins();
   // TODO(esprehn): WebPluginContainerImpl::SetCcLayer() also schedules a

third_party/blink/renderer/core/scheduler_integration_tests/scheduler_affecting_features_test.cc

@@ -150,8 +150,6 @@ TEST_F(SchedulingAffectingFeaturesTest, CacheControl_Navigation) {
 }
 
 TEST_F(SchedulingAffectingFeaturesTest, Plugins) {
-  scoped_feature_list_.InitAndEnableFeature(
-      features::kBackForwardCacheEnabledForNonPluginEmbed);
   {
     SimRequest main_resource("https://example.com/", "text/html");
     LoadURL("https://example.com/");
@@ -181,8 +179,6 @@ TEST_F(SchedulingAffectingFeaturesTest, Plugins) {
 }
 
 TEST_F(SchedulingAffectingFeaturesTest, NonPlugins) {
-  scoped_feature_list_.InitAndEnableFeature(
-      features::kBackForwardCacheEnabledForNonPluginEmbed);
   {
     SimRequest main_resource("https://example.com/", "text/html");
     LoadURL("https://example.com/");

third_party/blink/web_tests/FlagSpecificConfig

@@ -3,10 +3,6 @@
     "name": "back-forward-cache",
     "args": ["--enable-features=BackForwardCache"]
   },
-  {
-    "name": "back-forward-cache-embed",
-    "args": ["--enable-features=BackForwardCacheEnabledForNonPluginEmbed"]
-  },
   {
     "name": "disable-layout-ng",
     "args": ["--disable-blink-features=LayoutNG,LayoutNGBlockFragmentation"]