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

content/renderer/render_thread_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_thread_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <vector>
@@ skipping 876 matching lines @@
 scoped_refptr<base::MessageLoopProxy> RenderThreadImpl::GetIOLoopProxy() {
   return ChildProcess::current()->io_message_loop_proxy();
 }
 
 base::WaitableEvent* RenderThreadImpl::GetShutDownEvent() {
   return ChildProcess::current()->GetShutDownEvent();
 }
 
 scoped_ptr<base::SharedMemory> RenderThreadImpl::AllocateSharedMemory(
     uint32 size) {
+#if defined(OS_WIN)
+  scoped_ptr<base::SharedMemory> shared_memory(new base::SharedMemory);
+  if (!shared_memory->CreateAnonymous(size))

[jamesr, 2012/12/06 22:31:12]

content/renderer/pepper/pepper_plugin_delegate_impl creates shared memory in the
same was as this #else. Can we abstract this function int something shared and
use it from both RenderThreadImpl and PepperPluginDelegateImpl?

+    return scoped_ptr<base::SharedMemory>();
+
+  return scoped_ptr<base::SharedMemory>(shared_memory.release());
+#else
   base::SharedMemoryHandle handle;
   bool success;
   IPC::Message* message =
       new ChildProcessHostMsg_SyncAllocateSharedMemory(size, &handle);
 
   // Allow calling this from the compositor thread.
   if (MessageLoop::current() == message_loop())
     success = ChildThread::Send(message);
   else
     success = sync_message_filter()->Send(message);
 
   if (!success)
     return scoped_ptr<base::SharedMemory>();
 
   if (!base::SharedMemory::IsHandleValid(handle))
     return scoped_ptr<base::SharedMemory>();
   return scoped_ptr<base::SharedMemory>(new base::SharedMemory(handle, false));
+#endif  // defined(OS_WIN)
 }
 
 int32 RenderThreadImpl::CreateViewCommandBuffer(
       int32 surface_id, const GPUCreateCommandBufferConfig& init_params) {
   TRACE_EVENT1("gpu",
                "RenderThreadImpl::CreateViewCommandBuffer",
                "surface_id",
                surface_id);
 
   int32 route_id = MSG_ROUTING_NONE;
@@ skipping 184 matching lines @@
 RenderThreadImpl::GetFileThreadMessageLoopProxy() {
   DCHECK(message_loop() == MessageLoop::current());
   if (!file_thread_.get()) {
     file_thread_.reset(new base::Thread("Renderer::FILE"));
     file_thread_->Start();
   }
   return file_thread_->message_loop_proxy();
 }
 
 }  // namespace content