Map: Guard concurrent accesses to a std::map by a lock in drawing code.

chrome/browser/renderer_host/accelerated_surface_container_manager_mac.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_RENDERER_HOST_GPU_PLUGIN_CONTAINER_MANAGER_MAC_H_
 #define CHROME_BROWSER_RENDERER_HOST_GPU_PLUGIN_CONTAINER_MANAGER_MAC_H_
 #pragma once
 
 #include <OpenGL/OpenGL.h>
 #include <map>
 
 #include "app/surface/transport_dib.h"
 #include "base/basictypes.h"
+#include "base/lock.h"
 #include "gfx/native_widget_types.h"
 
 namespace webkit_glue {
 struct WebPluginGeometry;
 }
 
 class AcceleratedSurfaceContainerMac;
 
 // Helper class that manages the backing store and on-screen rendering
 // of instances of the GPU plugin on the Mac.
@@ skipping 75 matching lines @@
   // there will only be one container active when the accelerated
   // compositor is active.
   AcceleratedSurfaceContainerMac* root_container_;
   gfx::PluginWindowHandle root_container_handle_;
 
   // True if gpu rendering is active. The root container is created on demand
   // and destroyed only when a renderer process exits. When the compositor was
   // created, this is set to |false| while the compositor is not needed.
   bool gpu_rendering_active_;
 
+  // Both |plugin_window_to_container_map_| and the
+  // AcceleratedSurfaceContainerMac in it are not threadsafe, but accessed from
+  // multiple threads. All these accesses are guarded by this lock.
+  mutable Lock lock_;
+
   DISALLOW_COPY_AND_ASSIGN(AcceleratedSurfaceContainerManagerMac);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_GPU_PLUGIN_CONTAINER_MANAGER_MAC_H_