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

ui/gfx/gpu_memory_buffer.h

Index: ui/gfx/gpu_memory_buffer.h
diff --git a/ui/gfx/gpu_memory_buffer.h b/ui/gfx/gpu_memory_buffer.h
index 6d23c84ddc76074fc8bd5f13af1460e6b3c70531..28a5dc96a56ddeba0b560b11f4492077d171c2e1 100644
--- a/ui/gfx/gpu_memory_buffer.h
+++ b/ui/gfx/gpu_memory_buffer.h
@@ -102,6 +102,8 @@ class GFX_EXPORT GpuMemoryBuffer {
   // Returns the GUID for tracing.
   virtual base::trace_event::MemoryAllocatorDumpGuid GetGUIDForTracing(
       uint64_t tracing_process_id) const;
+
+  virtual base::SharedMemory* GetSharedMemory();
 };
 
 // Returns an instance of |handle| which can be sent over IPC. This duplicates