Add threaded compositing mode to field trial

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index e8b5dcbc5b6e19f672fe80df2a1df6617068b40d..b71f8d36bde0b0c8d2f8ee1bfec309164386a497 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -12,6 +12,7 @@
 #include "base/debug/trace_event.h"
 #include "base/i18n/rtl.h"
 #include "base/message_loop.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/utf_string_conversions.h"
@@ -34,6 +35,7 @@
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/user_metrics.h"
+#include "content/public/common/content_constants.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/result_codes.h"
 #include "skia/ext/image_operations.h"
@@ -1893,11 +1895,15 @@ void RenderWidgetHostImpl::AcknowledgeBufferPresent(
 }
 
 void RenderWidgetHostImpl::AcknowledgeSwapBuffersToRenderer() {
-  bool enable_threaded_compositing =
-      CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kEnableThreadedCompositing) &&
-      !CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kDisableThreadedCompositing);
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find(content::kGpuCompositingFieldTrialName);
+  bool thread_trial = trial && trial->group_name() ==
+      content::kGpuCompositingFieldTrialThreadEnabledName;
+  bool enable_threaded_compositing = thread_trial ||
+      (CommandLine::ForCurrentProcess()->HasSwitch(
+           switches::kEnableThreadedCompositing) &&
+       !CommandLine::ForCurrentProcess()->HasSwitch(
+           switches::kDisableThreadedCompositing));
   if (!enable_threaded_compositing)
     Send(new ViewMsg_SwapBuffers_ACK(routing_id_));
 }