Renderer process can allocate anonymous shared memory without help from browser process on Windows.

content/renderer/render_thread_impl.h

 // 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.
 
 #ifndef CONTENT_RENDERER_RENDER_THREAD_IMPL_H_
 #define CONTENT_RENDERER_RENDER_THREAD_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 99 matching lines @@
   virtual void SetOutgoingMessageFilter(
       IPC::ChannelProxy::OutgoingMessageFilter* filter) OVERRIDE;
   virtual void AddObserver(RenderProcessObserver* observer) OVERRIDE;
   virtual void RemoveObserver(RenderProcessObserver* observer) OVERRIDE;
   virtual void SetResourceDispatcherDelegate(
       ResourceDispatcherDelegate* delegate) OVERRIDE;
   virtual void WidgetHidden() OVERRIDE;
   virtual void WidgetRestored() OVERRIDE;
   virtual void EnsureWebKitInitialized() OVERRIDE;
   virtual void RecordUserMetrics(const std::string& action) OVERRIDE;
-  virtual base::SharedMemoryHandle HostAllocateSharedMemoryBuffer(
+  virtual scoped_ptr<base::SharedMemory> HostAllocateSharedMemoryBuffer(
       uint32 buffer_size) OVERRIDE;
   virtual void RegisterExtension(v8::Extension* extension) OVERRIDE;
   virtual void ScheduleIdleHandler(int64 initial_delay_ms) OVERRIDE;
   virtual void IdleHandler() OVERRIDE;
   virtual int64 GetIdleNotificationDelayInMs() const OVERRIDE;
   virtual void SetIdleNotificationDelayInMs(
       int64 idle_notification_delay_in_ms) OVERRIDE;
   virtual void ToggleWebKitSharedTimer(bool suspend) OVERRIDE;
   virtual void UpdateHistograms(int sequence_number) OVERRIDE;
 #if defined(OS_WIN)
@@ skipping 242 matching lines @@
   scoped_ptr<AudioRendererMixerManager> audio_renderer_mixer_manager_;
 
   HistogramCustomizer histogram_customizer_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderThreadImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_THREAD_IMPL_H_