Add threaded compositing mode to field trial

content/renderer/render_thread_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/render_thread_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <vector>
@@ skipping 22 matching lines @@
 #include "content/common/gpu/client/gpu_channel_host.h"
 #include "content/common/gpu/gpu_messages.h"
 #include "content/common/indexed_db/indexed_db_dispatcher.h"
 #include "content/common/indexed_db/indexed_db_message_filter.h"
 #include "content/common/npobject_util.h"
 #include "content/common/plugin_messages.h"
 #include "content/common/resource_dispatcher.h"
 #include "content/common/resource_messages.h"
 #include "content/common/view_messages.h"
 #include "content/common/web_database_observer_impl.h"
+#include "content/public/common/content_constants.h"
 #include "content/public/common/content_paths.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/common/renderer_preferences.h"
 #include "content/public/common/url_constants.h"
 #include "content/public/renderer/content_renderer_client.h"
 #include "content/public/renderer/render_process_observer.h"
 #include "content/public/renderer/render_view_visitor.h"
 #include "content/renderer/browser_plugin/old/browser_plugin_channel_manager.h"
 #include "content/renderer/browser_plugin/old/browser_plugin_registry.h"
 #include "content/renderer/devtools_agent_filter.h"
@@ skipping 432 matching lines @@
   ScheduleIdleHandler(kLongIdleHandlerDelayMs);
 }
 
 void RenderThreadImpl::EnsureWebKitInitialized() {
   if (webkit_platform_support_.get())
     return;
 
   webkit_platform_support_.reset(new RendererWebKitPlatformSupportImpl);
   WebKit::initialize(webkit_platform_support_.get());
 
+  base::FieldTrial* thread_trial =
+      base::FieldTrialList::Find(content::kGpuCompositingFieldTrialName);
+  bool is_thread_trial = thread_trial && thread_trial->group_name() ==
+      content::kGpuCompositingFieldTrialThreadEnabledName;
   bool has_enable = CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kEnableThreadedCompositing);
   bool has_disable = CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kDisableThreadedCompositing);
   // TODO(fsamuel): Guests don't currently support threaded compositing.
   // This should go away with the new design of the browser plugin.
   // The new design can be tracked at: http://crbug.com/134492.
   bool is_guest = CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kGuestRenderer);
-  bool enable = has_enable && (!has_disable) && (!is_guest);
+  bool enable = (is_thread_trial || (has_enable && !has_disable)) && !is_guest;

[Ilya Sherman, 2012/07/20 05:36:05]

Is it correct that the field trial should override the "disable" flag?  I would
have expected the flag to take precedence.

Actually, it looks like this is currently enforced within gpu_util when setting
up the trial -- maybe there should be a DCHECK here to double-check that
invariant?

(Same applies to the change in render_widget_host_impl.cc)

[jbates, 2012/07/23 17:47:00]

Done.

   if (enable) {
     compositor_thread_.reset(new CompositorThread(this));
     AddFilter(compositor_thread_->GetMessageFilter());
     WebKit::WebCompositor::initialize(compositor_thread_->GetWebThread());
   } else
     WebKit::WebCompositor::initialize(NULL);

[Ilya Sherman, 2012/07/20 05:36:05]

nit: As long as you're editing nearby code, please add curly braces to the else
stmt, since the if-stmt needs them.

[jbates, 2012/07/23 17:47:00]

Done.

   compositor_initialized_ = true;
 
   WebScriptController::enableV8SingleThreadMode();
 
   RenderThreadImpl::RegisterSchemes();
 
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
 
   webkit_glue::EnableWebCoreLogChannels(
       command_line.GetSwitchValueASCII(switches::kWebCoreLogChannels));
@@ skipping 523 matching lines @@
 
 scoped_refptr<base::MessageLoopProxy>
 RenderThreadImpl::GetFileThreadMessageLoopProxy() {
   DCHECK(message_loop() == MessageLoop::current());
   if (!file_thread_.get()) {
     file_thread_.reset(new base::Thread("Renderer::FILE"));
     file_thread_->Start();
   }
   return file_thread_->message_loop_proxy();
 }