Fix webrtc HW encode deadlock scenarios.

content/renderer/media/renderer_gpu_video_accelerator_factories.cc

Index: content/renderer/media/renderer_gpu_video_accelerator_factories.cc
diff --git a/content/renderer/media/renderer_gpu_video_accelerator_factories.cc b/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
index f586497f484a8b83135f7ec82c213096ddf76aac..40325beafcf2ae28b2a12f1c51f403cb46b2a569 100644
--- a/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
+++ b/content/renderer/media/renderer_gpu_video_accelerator_factories.cc
@@ -51,6 +51,12 @@ RendererGpuVideoAcceleratorFactories::RendererGpuVideoAcceleratorFactories(
                  // returns, so our PostTask will run first.
                  context));
   message_loop_async_waiter_.Wait();
+
+  shm_alloc_thread_.reset(
+      new base::Thread("RendererGpuVideoAccelFactsSHMAllocThread"));
+  CHECK(shm_alloc_thread_->Start());
+
+  shm_alloc_message_loop_ = shm_alloc_thread_->message_loop_proxy();
 }
 
 RendererGpuVideoAcceleratorFactories::RendererGpuVideoAcceleratorFactories()
@@ -363,10 +369,10 @@ void RendererGpuVideoAcceleratorFactories::AsyncReadPixels(
 
 base::SharedMemory* RendererGpuVideoAcceleratorFactories::CreateSharedMemory(
     size_t size) {
-  if (main_message_loop_->BelongsToCurrentThread()) {
+  if (shm_alloc_message_loop_->BelongsToCurrentThread()) {
     return ChildThread::current()->AllocateSharedMemory(size);
   }
-  main_message_loop_->PostTask(
+  shm_alloc_message_loop_->PostTask(
       FROM_HERE,
       base::Bind(&RendererGpuVideoAcceleratorFactories::AsyncCreateSharedMemory,
                  this,
@@ -381,11 +387,10 @@ base::SharedMemory* RendererGpuVideoAcceleratorFactories::CreateSharedMemory(
 
 void RendererGpuVideoAcceleratorFactories::AsyncCreateSharedMemory(
     size_t size) {
-  DCHECK_EQ(base::MessageLoop::current(),
-            ChildThread::current()->message_loop());
+  DCHECK(shm_alloc_message_loop_->BelongsToCurrentThread());
 
-  shared_memory_segment_.reset(
-      ChildThread::current()->AllocateSharedMemory(size));
+  shared_memory_segment_.reset(new base::SharedMemory());
+  CHECK(shared_memory_segment_->CreateAndMapAnonymous(size));

[Ami GONE FROM CHROMIUM, 2013/09/04 20:47:56]

Do you even sandbox, bro?
How is this working inside the renderer sandbox?
https://code.google.com/p/chromium/codesearch#chromium/src/content/child/chil...

If you _could_ create shm's on arbitrary renderer-process threads (as this CL
implies, and which I think should actually be possible if you use a thread-safe
IPC sender and the static ChildThread::AllocateSharedMemory() overload) then you
wouldn't need the trampoline in the first place - just do the create from the
calling thread!

[Pawel Osciak, 2013/09/05 05:46:33]

Real men don't sandbox. Done for all the others.

   render_thread_async_waiter_.Signal();

[Ami GONE FROM CHROMIUM, 2013/09/04 20:47:56]

This is not legit considering it's no longer the render_thread we're running on
(so, for example, two outstanding operations could be extant, one to the render
thread and one to here, and this signal would terminate both waits, and so on). 
But if you take my suggestion above then this code is deleted and no worries.

[Pawel Osciak, 2013/09/05 05:46:33]

Done.

 }
 
@@ -408,6 +413,7 @@ RendererGpuVideoAcceleratorFactories::Clone() {
   factories->main_message_loop_ = main_message_loop_;
   factories->gpu_channel_host_ = gpu_channel_host_;
   factories->context_ = context_;
+  factories->shm_alloc_message_loop_ = shm_alloc_message_loop_;
   return factories;
 }