Add a runtime enabled feature flag for raster-inducing scroll

In order to make sure that nothing breaks during our implementation of
raster-inducing scroll, we should just hide this new feature behind a
flag.

Bug: 820048
Change-Id: I38b446cff82aa5f4c9e23b5fdb04f5895d218e2a
Reviewed-on: https://chromium-review.googlesource.com/955666Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541842}

content/child/runtime_features.cc

@@ -338,6 +338,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
                                                 false);
   }
 
+  if (base::FeatureList::IsEnabled(features::kRasterInducingScroll))
+    WebRuntimeFeatures::EnableRasterInducingScroll(true);
+
   WebRuntimeFeatures::EnableFeatureFromString(
       "AllowContentInitiatedDataUrlNavigations",
       base::FeatureList::IsEnabled(

content/public/common/content_features.cc

@@ -286,6 +286,10 @@ const base::Feature kPurgeAndSuspend {
 const base::Feature kPWAFullCodeCache{"PWAFullCodeCache",
                                       base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enable raster-inducing scroll.
+const base::Feature kRasterInducingScroll{"RasterInducingScroll",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Throttle Blink's rendering pipeline based on frame visibility.
 const base::Feature kRenderingPipelineThrottling{
     "RenderingPipelineThrottling", base::FEATURE_ENABLED_BY_DEFAULT};

content/public/common/content_features.h

@@ -70,6 +70,7 @@ CONTENT_EXPORT extern const base::Feature kPassiveEventListenersDueToFling;
 CONTENT_EXPORT extern const base::Feature kPepper3DImageChromium;
 CONTENT_EXPORT extern const base::Feature kPurgeAndSuspend;
 CONTENT_EXPORT extern const base::Feature kPWAFullCodeCache;
+CONTENT_EXPORT extern const base::Feature kRasterInducingScroll;
 CONTENT_EXPORT extern const base::Feature kRenderingPipelineThrottling;
 CONTENT_EXPORT extern const base::Feature kReportRendererPeakMemoryStats;
 CONTENT_EXPORT extern const base::Feature kRequireCSSExtensionForFile;

third_party/WebKit/Source/platform/exported/WebRuntimeFeatures.cpp

@@ -260,6 +260,10 @@ void WebRuntimeFeatures::EnablePreloadDefaultIsMetadata(bool enable) {
   RuntimeEnabledFeatures::SetPreloadDefaultIsMetadataEnabled(enable);
 }
 
+void WebRuntimeFeatures::EnableRasterInducingScroll(bool enable) {
+  RuntimeEnabledFeatures::SetRasterInducingScrollEnabled(enable);
+}
+
 void WebRuntimeFeatures::EnableScriptedSpeech(bool enable) {
   RuntimeEnabledFeatures::SetScriptedSpeechEnabled(enable);
 }

third_party/WebKit/Source/platform/runtime_enabled_features.json5

@@ -880,6 +880,10 @@
     {
       name: "PWAFullCodeCache"
     },
+    {
+      name: "RasterInducingScroll",
+      status: "experimental",
+    },
     {
       name: "ReducedReferrerGranularity",
     },

third_party/WebKit/public/platform/WebRuntimeFeatures.h

@@ -118,6 +118,7 @@ class WebRuntimeFeatures {
   BLINK_PLATFORM_EXPORT static void EnablePrintBrowser(bool);
   BLINK_PLATFORM_EXPORT static void EnablePresentationAPI(bool);
   BLINK_PLATFORM_EXPORT static void EnablePushMessaging(bool);
+  BLINK_PLATFORM_EXPORT static void EnableRasterInducingScroll(bool);
   BLINK_PLATFORM_EXPORT static void EnableReducedReferrerGranularity(bool);
   BLINK_PLATFORM_EXPORT static void EnableRemotePlaybackAPI(bool);
   BLINK_PLATFORM_EXPORT static void EnableRenderingPipelineThrottling(bool);