Enables compositing support for webview.

Mailboxes for the webview are received from RWHVGuest and set on the
texture layer with a callback that gets triggered when they are no
longer in use by the compositor.

An IPC is sent back to the browser with a sync point to ack
the presented buffer.

BUG=143429


Review URL: https://chromiumcodereview.appspot.com/11824040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@176310 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index 8f7cf38..0d14684 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -597,13 +597,7 @@
       WebKit::Platform::current()->compositorSupport();
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
 
-  // 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 = command_line.HasSwitch(switches::kGuestRenderer);
-  bool threaded = command_line.HasSwitch(switches::kEnableThreadedCompositing);
-
-  bool enable = threaded && !is_guest;
+  bool enable = command_line.HasSwitch(switches::kEnableThreadedCompositing);
   if (enable) {
     compositor_thread_.reset(new CompositorThread(this));
     AddFilter(compositor_thread_->GetMessageFilter());