Add a flag to enable remote CoreAnimation API.

ui/base/cocoa/remote_layer_api.mm

Index: ui/base/cocoa/remote_layer_api.mm
diff --git a/ui/base/cocoa/remote_layer_api.mm b/ui/base/cocoa/remote_layer_api.mm
index c58402ffe9ae3e84d0d3a4134c739f39810d1840..0fb1fdff4804ee0a9b5559e6960bf81ea1d2a990 100644
--- a/ui/base/cocoa/remote_layer_api.mm
+++ b/ui/base/cocoa/remote_layer_api.mm
@@ -4,11 +4,20 @@
 
 #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() {
+  bool enabled_at_command_line =
+      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)