gpu: Implement idle async pixel transfers.

ui/gl/async_pixel_transfer_delegate.h

 // Copyright (c) 2011 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 UI_GL_ASYNC_TASK_DELEGATE_H_
 #define UI_GL_ASYNC_TASK_DELEGATE_H_
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 94 matching lines @@
       const AsyncTexSubImage2DParams& tex_params,
       const AsyncMemoryParams& mem_params) = 0;
 
   // Block until the specified transfer completes.
   virtual void WaitForTransferCompletion(
       AsyncPixelTransferState* state) = 0;
 
   virtual uint32 GetTextureUploadCount() = 0;
   virtual base::TimeDelta GetTotalTextureUploadTime() = 0;
 
+  // ProcessPendingTransfers() will be called at a good time
+  // to process a small amount of pending transfer work while
+  // NeedsProcessPendingTransfers() returns true. Implementations
+  // that can't dispatch work to separate threads should use
+  // this to avoid blocking the caller thread inappropriately.
+  virtual void ProcessPendingTransfers() = 0;
+  virtual bool NeedsProcessPendingTransfers() = 0;
+
  protected:
   AsyncPixelTransferDelegate() {}
   // For testing, as returning scoped_ptr wouldn't work with MOCK_METHOD.
   virtual AsyncPixelTransferState*
       CreateRawPixelTransferState(GLuint tex_id,
           const AsyncTexImage2DParams& define_params) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AsyncPixelTransferDelegate);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_ASYNC_TASK_DELEGATE_H_