[WIP] Add SharedMemoryTracker to dump base::SharedMemory usage

gpu/command_buffer/common/buffer.h

Index: gpu/command_buffer/common/buffer.h
diff --git a/gpu/command_buffer/common/buffer.h b/gpu/command_buffer/common/buffer.h
index d4de9175471160c9cd478e690978d50b0d207764..90b60e5dbc6a585050c4204389fcd0055068491a 100644
--- a/gpu/command_buffer/common/buffer.h
+++ b/gpu/command_buffer/common/buffer.h
@@ -25,7 +25,7 @@ namespace gpu {
 class GPU_EXPORT BufferBacking {
  public:
   virtual ~BufferBacking() {}
-  virtual bool is_shared() const;
+  virtual base::SharedMemory* shared_memory();
   virtual void* GetMemory() const = 0;
   virtual size_t GetSize() const = 0;
 };
@@ -35,10 +35,9 @@ class GPU_EXPORT SharedMemoryBufferBacking : public BufferBacking {
   SharedMemoryBufferBacking(std::unique_ptr<base::SharedMemory> shared_memory,
                             size_t size);
   ~SharedMemoryBufferBacking() override;
-  bool is_shared() const override;
+  base::SharedMemory* shared_memory() override;
   void* GetMemory() const override;
   size_t GetSize() const override;
-  base::SharedMemory* shared_memory() { return shared_memory_.get(); }
 
  private:
   std::unique_ptr<base::SharedMemory> shared_memory_;