Add a flag to enable impl-thread event handling on Mac

content/renderer/render_view_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_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/auto_reset.h"
@@ skipping 2116 matching lines @@
 }
 
 void RenderViewImpl::initializeLayerTreeView() {
   RenderWidget::initializeLayerTreeView();
   RenderWidgetCompositor* rwc = compositor();
   if (!rwc)
     return;
   if (webview() && webview()->devToolsAgent())
     webview()->devToolsAgent()->setLayerTreeId(rwc->GetLayerTreeId());
 
-#if !defined(OS_MACOSX)  // many events are unhandled - http://crbug.com/138003
-  RenderThreadImpl* render_thread = RenderThreadImpl::current();
-  // render_thread may be NULL in tests.
-  InputHandlerManager* input_handler_manager =
-      render_thread ? render_thread->input_handler_manager() : NULL;
-  if (input_handler_manager) {
-    input_handler_manager->AddInputHandler(
-        routing_id_, rwc->GetInputHandler(), AsWeakPtr());
+  bool use_threaded_event_handling = true;
+#if defined(OS_MACOSX)
+  // Development flag because many events are still unhandled on Mac.
+  // http://crbug.com/138003
+  use_threaded_event_handling = CommandLine::ForCurrentProcess()->HasSwitch(
+      switches::kEnableThreadedEventHandlingMac);
+#endif
+  if (use_threaded_event_handling) {
+    RenderThreadImpl* render_thread = RenderThreadImpl::current();
+    // render_thread may be NULL in tests.
+    InputHandlerManager* input_handler_manager =
+        render_thread ? render_thread->input_handler_manager() : NULL;
+    if (input_handler_manager) {
+      input_handler_manager->AddInputHandler(
+          routing_id_, rwc->GetInputHandler(), AsWeakPtr());
+    }
   }
-#endif
 }
 
 // blink::WebFrameClient -----------------------------------------------------
 
 void RenderViewImpl::Repaint(const gfx::Size& size) {
   OnRepaint(size);
 }
 
 void RenderViewImpl::SetEditCommandForNextKeyEvent(const std::string& name,
                                                    const std::string& value) {
@@ skipping 2038 matching lines @@
     std::vector<gfx::Size> sizes;
     ConvertToFaviconSizes(icon_urls[i].sizes(), &sizes);
     if (!url.isEmpty())
       urls.push_back(
           FaviconURL(url, ToFaviconType(icon_urls[i].iconType()), sizes));
   }
   SendUpdateFaviconURL(urls);
 }
 
 }  // namespace content