Add TransferBufferInterface::shared_memory_handle()

gpu/command_buffer/client/transfer_buffer.h

Index: gpu/command_buffer/client/transfer_buffer.h
diff --git a/gpu/command_buffer/client/transfer_buffer.h b/gpu/command_buffer/client/transfer_buffer.h
index 5f6623e05124e28dbb8f3985d9c3c0972367ee11..155e8b0094e1fdfd6dce614a74d6e7e62e6f2043 100644
--- a/gpu/command_buffer/client/transfer_buffer.h
+++ b/gpu/command_buffer/client/transfer_buffer.h
@@ -17,6 +17,12 @@
 #include "gpu/command_buffer/common/gles2_cmd_utils.h"
 #include "gpu/gpu_export.h"
 
+namespace base {
+
+class SharedMemoryHandle;
+
+}  // namespace base
+
 namespace gpu {
 
 class CommandBufferHelper;
@@ -27,6 +33,10 @@ class GPU_EXPORT TransferBufferInterface {
   TransferBufferInterface() { }
   virtual ~TransferBufferInterface() { }
 
+  // Returns the shared memory's handle when the back end is base::SharedMemory.
+  // Otherwise, this returns an invalid handle.
+  virtual base::SharedMemoryHandle shared_memory_handle() const = 0;
+
   virtual bool Initialize(
       unsigned int buffer_size,
       unsigned int result_size,
@@ -68,6 +78,7 @@ class GPU_EXPORT TransferBuffer : public TransferBufferInterface {
   ~TransferBuffer() override;
 
   // Overridden from TransferBufferInterface.
+  base::SharedMemoryHandle shared_memory_handle() const override;
   bool Initialize(unsigned int default_buffer_size,
                   unsigned int result_size,
                   unsigned int min_buffer_size,