Add cc::SharedBitmap::shared_memory_handle()

cc/resources/shared_bitmap.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 CC_RESOURCES_SHARED_BITMAP_H_
 #define CC_RESOURCES_SHARED_BITMAP_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/trace_event/memory_allocator_dump.h"
 #include "cc/cc_export.h"
 #include "gpu/command_buffer/common/mailbox.h"
 #include "ui/gfx/geometry/size.h"
 
+namespace base {
+class SharedMemoryHandle;
+}
+
 namespace cc {
 typedef gpu::Mailbox SharedBitmapId;
 
 CC_EXPORT base::trace_event::MemoryAllocatorDumpGuid
 GetSharedBitmapGUIDForTracing(const SharedBitmapId& bitmap_id);
 
 class CC_EXPORT SharedBitmap {
  public:
   SharedBitmap(uint8_t* pixels, const SharedBitmapId& id);
 
   virtual ~SharedBitmap();
 
   uint8_t* pixels() { return pixels_; }
 
   const SharedBitmapId& id() { return id_; }
 
+  // Returns the shared memory's handle when the back end is base::SharedMemory.
+  // Otherwise, this returns an invalid handle.
+  virtual base::SharedMemoryHandle GetSharedMemoryHandle() const = 0;
+
   // Returns true if the size is valid and false otherwise.
   static bool SizeInBytes(const gfx::Size& size, size_t* size_in_bytes);
   // Dies with a CRASH() if the size can not be represented as a positive number
   // of bytes.
   static size_t CheckedSizeInBytes(const gfx::Size& size);
   // Returns the size in bytes but may overflow or return 0. Only do this for
   // sizes that have already been checked.
   static size_t UncheckedSizeInBytes(const gfx::Size& size);
   // Returns true if the size is valid and false otherwise.
   static bool VerifySizeInBytes(const gfx::Size& size);
 
   static SharedBitmapId GenerateId();
 
  private:
   uint8_t* pixels_;
   SharedBitmapId id_;
 
   DISALLOW_COPY_AND_ASSIGN(SharedBitmap);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_SHARED_BITMAP_H_