Introduce command buffer control thread

mojo/services/gles2/gpu_impl.h

Index: mojo/services/gles2/gpu_impl.h
diff --git a/mojo/services/gles2/gpu_impl.h b/mojo/services/gles2/gpu_impl.h
index 62a8af69c5407a8049805dc3c9abc45faf8c7fab..2edb2019b2ab407abe056333d3ae4093782c3794 100644
--- a/mojo/services/gles2/gpu_impl.h
+++ b/mojo/services/gles2/gpu_impl.h
@@ -4,6 +4,7 @@
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/threading/thread.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 #include "mojo/public/cpp/bindings/strong_binding.h"
 #include "mojo/services/public/interfaces/geometry/geometry.mojom.h"
@@ -24,10 +25,36 @@ namespace mojo {
 
 class GpuImpl : public Gpu {
  public:
-  GpuImpl(InterfaceRequest<Gpu> request,
-          const scoped_refptr<gfx::GLShareGroup>& share_group,
-          const scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager);
+  // We need to share these across all CommandBuffer instances so that contexts
+  // they create can share resources with each other via mailboxes.
+  class State : public base::RefCounted<State> {
+   public:
+    State();
+
+    // We run the CommandBufferImpl on the control_task_runner, which forwards
+    // most method class to the CommandBufferDriver, which runs on the "driver",
+    // thread (i.e., the thread on which GpuImpl instances are created).
+    scoped_refptr<base::SingleThreadTaskRunner> control_task_runner() {
+      return control_thread_.task_runner();
+    }
+
+    // These objects are intended to be used on the "driver" thread (i.e., the
+    // thread on which GpuImpl instances are created).
+    gfx::GLShareGroup* share_group() const { return share_group_.get(); }
+    gpu::gles2::MailboxManager* mailbox_manager() const {
+      return mailbox_manager_.get();
+    }
+
+   private:
+    friend class base::RefCounted<State>;
+    ~State();
 
+    base::Thread control_thread_;
+    scoped_refptr<gfx::GLShareGroup> share_group_;
+    scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager_;
+  };
+
+  GpuImpl(InterfaceRequest<Gpu> request, const scoped_refptr<State>& state);
   ~GpuImpl() override;
 
   void CreateOnscreenGLES2Context(
@@ -39,12 +66,8 @@ class GpuImpl : public Gpu {
       InterfaceRequest<CommandBuffer> command_buffer_request) override;
 
  private:
-  // We need to share these across all CommandBuffer instances so that contexts
-  // they create can share resources with each other via mailboxes.
-  scoped_refptr<gfx::GLShareGroup> share_group_;
-  scoped_refptr<gpu::gles2::MailboxManager> mailbox_manager_;
-
   StrongBinding<Gpu> binding_;
+  scoped_refptr<State> state_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuImpl);
 };