Add a flag to enable remote CoreAnimation API.

ui/base/cocoa/remote_layer_api.mm

 // Copyright 2014 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 "ui/base/cocoa/remote_layer_api.h"
 
+#include "base/command_line.h"
+#include "ui/base/ui_base_switches.h"
+
 #include <objc/runtime.h>
 
 namespace ui {
 
 bool RemoteLayerAPISupported() {
+  static bool enabled_at_command_line =

[sky, 2014/08/14 00:19:08]

Unless there is really a reason to make this static I wouldn't. Otherwise unit
tests may be tricky.

[ccameron, 2014/08/14 00:33:31]

Done.

+      CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableRemoteCoreAnimation);
+  if (!enabled_at_command_line)
+    return false;
+
   // Verify the GPU process interfaces are present.
   static Class caContextClass = NSClassFromString(@"CAContext");
   if (!caContextClass)
     return false;
 
   // Note that because the contextId and layer properties are dynamic,
   // instancesRespondToSelector will return NO for them.
   static bool caContextClassValid =
       [caContextClass respondsToSelector:
           @selector(contextWithCGSConnection:options:)] &&
@@ skipping 12 matching lines @@
       [caLayerHostClass instancesRespondToSelector:@selector(setContextId:)];
   if (!caLayerHostClassValid)
     return false;
 
   // If everything is there, we should be able to use the API.
   return true;
 }
 
 }  // namespace