exo: Directly create GpuMemoryBufferImpl when a handle is available.

gpu/ipc/client/gpu_memory_buffer_impl.h

 // Copyright 2013 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 GPU_IPC_CLIENT_GPU_MEMORY_BUFFER_IMPL_H_
 #define GPU_IPC_CLIENT_GPU_MEMORY_BUFFER_IMPL_H_
 
 #include <memory>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "gpu/command_buffer/common/sync_token.h"
 #include "gpu/gpu_export.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace gpu {
 
 // Provides common implementation of a GPU memory buffer.
 class GPU_EXPORT GpuMemoryBufferImpl : public gfx::GpuMemoryBuffer {
  public:
   typedef base::Callback<void(const gpu::SyncToken& sync)> DestructionCallback;
 
   ~GpuMemoryBufferImpl() override;
 
   // Creates an instance from the given |handle|. |size| and |internalformat|
-  // should match what was used to allocate the |handle|. |callback| is
-  // called when instance is deleted, which is not necessarily on the same
-  // thread as this function was called on and instance was created on.
+  // should match what was used to allocate the |handle|. |callback|, if
+  // non-null, is called when instance is deleted, which is not necessarily on
+  // the same thread as this function was called on and instance was created on.
   static std::unique_ptr<GpuMemoryBufferImpl> CreateFromHandle(
       const gfx::GpuMemoryBufferHandle& handle,
       const gfx::Size& size,
       gfx::BufferFormat format,
       gfx::BufferUsage usage,
       const DestructionCallback& callback);
 
   // Overridden from gfx::GpuMemoryBuffer:
   gfx::Size GetSize() const override;
   gfx::BufferFormat GetFormat() const override;
@@ skipping 17 matching lines @@
   bool mapped_;
   gpu::SyncToken destruction_sync_token_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GpuMemoryBufferImpl);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_CLIENT_GPU_MEMORY_BUFFER_IMPL_H_