Introduce command buffer control thread

mojo/services/gles2/command_buffer_impl.h

 // Copyright 2014 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 MOJO_SERVICES_GLES2_COMMAND_BUFFER_IMPL_H_
 #define MOJO_SERVICES_GLES2_COMMAND_BUFFER_IMPL_H_
 
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/single_thread_task_runner.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "mojo/services/public/interfaces/gpu/command_buffer.mojom.h"
 
 namespace mojo {
 class CommandBufferDriver;
 
+// This class listens to the CommandBuffer message pipe on a low-latency thread
+// so that we can insert sync points without blocking on the GL driver. It
+// forwards most method calls to the CommandBufferDriver, which runs on the
+// same thread as the native viewport.
 class CommandBufferImpl : public CommandBuffer {
  public:
-  CommandBufferImpl(InterfaceRequest<CommandBuffer> request,
-                    scoped_ptr<CommandBufferDriver> driver);
+  CommandBufferImpl(
+      InterfaceRequest<CommandBuffer> request,
+      scoped_refptr<base::SingleThreadTaskRunner> control_task_runner,
+      scoped_ptr<CommandBufferDriver> driver);
   ~CommandBufferImpl() override;
 
   void Initialize(CommandBufferSyncClientPtr sync_client,
-                  mojo::ScopedSharedBufferHandle shared_state) override;
+                  ScopedSharedBufferHandle shared_state) override;
   void SetGetBuffer(int32_t buffer) override;
   void Flush(int32_t put_offset) override;
   void MakeProgress(int32_t last_get_offset) override;
   void RegisterTransferBuffer(int32_t id,
-                              mojo::ScopedSharedBufferHandle transfer_buffer,
+                              ScopedSharedBufferHandle transfer_buffer,
                               uint32_t size) override;
   void DestroyTransferBuffer(int32_t id) override;
   void Echo(const Callback<void()>& callback) override;
 
  private:
+  void BindToRequest(InterfaceRequest<CommandBuffer> request);
   void OnContextLost(int32_t reason);
 
+  scoped_refptr<base::SingleThreadTaskRunner> driver_task_runner_;
+  scoped_ptr<CommandBufferDriver> driver_;
+
   StrongBinding<CommandBuffer> binding_;
-  scoped_ptr<CommandBufferDriver> driver_;
+  base::WeakPtrFactory<CommandBufferImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CommandBufferImpl);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_SERVICES_GLES2_COMMAND_BUFFER_IMPL_H_