Expose --disable-gpu-compositing browser arg to Blink

Currently in Blink, there is no indication whether a compositor is GPU
accelerated or software. This CL plumbs it to Blink, so that we can
query whether --disable-gpu-compositing or --disable-gpu is set or not.

BUG=650795

Review-Url: https://codereview.chromium.org/2377883002
Cr-Commit-Position: refs/heads/master@{#422672}

content/child/runtime_features.cc

@@ -117,6 +117,12 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
   if (command_line.HasSwitch(switches::kForceDisplayList2dCanvas))
     WebRuntimeFeatures::forceDisplayList2dCanvas(true);
 
+  if (command_line.HasSwitch(switches::kDisableGpuCompositing) ||
+      command_line.HasSwitch(switches::kDisableGpu))
+    WebRuntimeFeatures::enableGpuCompositing(false);
+  else
+    WebRuntimeFeatures::enableGpuCompositing(true);
+
   if (command_line.HasSwitch(
       switches::kEnableCanvas2dDynamicRenderingModeSwitching))
     WebRuntimeFeatures::enableCanvas2dDynamicRenderingModeSwitching(true);

third_party/WebKit/Source/platform/RuntimeEnabledFeatures.in

@@ -105,6 +105,7 @@ GamepadExtensions
 GeometryInterfaces status=experimental, implied_by=CompositorWorker
 GetUserMedia status=stable
 GlobalCacheStorage status=stable
+GpuCompositing
 IDBObserver status=experimental
 ImageCapture status=experimental
 ImageOrientation status=test

third_party/WebKit/Source/web/WebRuntimeFeatures.cpp

@@ -104,6 +104,10 @@ void WebRuntimeFeatures::enableDisplayList2dCanvas(bool enable) {
   RuntimeEnabledFeatures::setDisplayList2dCanvasEnabled(enable);
 }
 
+void WebRuntimeFeatures::enableGpuCompositing(bool enable) {
+  RuntimeEnabledFeatures::setGpuCompositingEnabled(enable);
+}
+
 void WebRuntimeFeatures::enableCanvas2dDynamicRenderingModeSwitching(
     bool enable) {
   RuntimeEnabledFeatures::setEnableCanvas2dDynamicRenderingModeSwitchingEnabled(

third_party/WebKit/public/web/WebRuntimeFeatures.h

@@ -81,6 +81,7 @@ class WebRuntimeFeatures {
   BLINK_EXPORT static void enableFeaturePolicy(bool);
   BLINK_EXPORT static void enableFileSystem(bool);
   BLINK_EXPORT static void enableGamepadExtensions(bool);
+  BLINK_EXPORT static void enableGpuCompositing(bool);
   BLINK_EXPORT static void enableInputMultipleFieldsUI(bool);
   BLINK_EXPORT static void enableMediaCapture(bool);
   BLINK_EXPORT static void enableMediaDocumentDownloadButton(bool);