Add WorkStealingInScriptRunner feature flag.

This mirrors the existing Blink feature flag, in order to support runtime
experiments with this feature.

Bug: 557466
Change-Id: Ifa74a5ac15b35474bda14abca9aea40755f48c5c
Reviewed-on: https://chromium-review.googlesource.com/642966
Commit-Queue: Daniel Vogelheim <vogelheim@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510081}

content/child/runtime_features.cc

@@ -386,6 +386,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   WebRuntimeFeatures::EnableModernMediaControls(
       base::FeatureList::IsEnabled(media::kUseModernMediaControls));
 
+  WebRuntimeFeatures::EnableWorkStealingInScriptRunner(
+      base::FeatureList::IsEnabled(features::kWorkStealingInScriptRunner));
+
   // Enable explicitly enabled features, and then disable explicitly disabled
   // ones.
   for (const std::string& feature :

content/public/common/content_features.cc

@@ -416,6 +416,10 @@ const base::Feature kKeepAliveRendererForKeepaliveRequests{
 const base::Feature kWebVRExperimentalRendering{
     "WebVRExperimentalRendering", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Enabled "work stealing" in the script runner.
+const base::Feature kWorkStealingInScriptRunner{
+    "WorkStealingInScriptRunner", base::FEATURE_DISABLED_BY_DEFAULT};
+
 #if defined(OS_ANDROID)
 // Autofill Accessibility in Android.
 // crbug.com/627860

content/public/common/content_features.h

@@ -103,6 +103,7 @@ CONTENT_EXPORT extern const base::Feature kWebRtcUseEchoCanceller3;
 CONTENT_EXPORT extern const base::Feature kWebRtcUseGpuMemoryBufferVideoFrames;
 CONTENT_EXPORT extern const base::Feature kWebUsb;
 CONTENT_EXPORT extern const base::Feature kWebVRExperimentalRendering;
+CONTENT_EXPORT extern const base::Feature kWorkStealingInScriptRunner;
 
 #if defined(OS_ANDROID)
 CONTENT_EXPORT extern const base::Feature kAndroidAutofillAccessibility;

testing/variations/fieldtrial_testing_config.json

@@ -3939,6 +3939,25 @@
             ]
         }
     ],
+    "WorkStealingInScriptRunner": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "linux",
+                "mac",
+                "win"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "WorkStealingInScriptRunner"
+                    ]
+                }
+            ]
+        }
+    ],
     "YieldBetweenContentScriptRuns": [
         {
             "platforms": [

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

@@ -470,4 +470,8 @@ void WebRuntimeFeatures::EnableAutomationControlled(bool enable) {
   RuntimeEnabledFeatures::SetAutomationControlledEnabled(enable);
 }
 
+void WebRuntimeFeatures::EnableWorkStealingInScriptRunner(bool enable) {
+  RuntimeEnabledFeatures::SetWorkStealingInScriptRunnerEnabled(enable);
+}
+
 }  // namespace blink

third_party/WebKit/public/platform/WebRuntimeFeatures.h

@@ -179,6 +179,7 @@ class WebRuntimeFeatures {
       bool);
   BLINK_PLATFORM_EXPORT static void EnableV8ContextSnapshot(bool);
   BLINK_PLATFORM_EXPORT static void EnableAutomationControlled(bool);
+  BLINK_PLATFORM_EXPORT static void EnableWorkStealingInScriptRunner(bool);
 
  private:
   WebRuntimeFeatures();