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

ui/gfx/gpu_memory_buffer.cc

 // 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.
 
 #include "ui/gfx/gpu_memory_buffer.h"
 
 #include "ui/gfx/generic_shared_memory_id.h"
 
 namespace gfx {
 
@@ skipping 37 matching lines @@
   }
   return gfx::GpuMemoryBufferHandle();
 }
 
 base::trace_event::MemoryAllocatorDumpGuid GpuMemoryBuffer::GetGUIDForTracing(
     uint64_t tracing_process_id) const {
   return gfx::GetGenericSharedGpuMemoryGUIDForTracing(tracing_process_id,
                                                       GetId());
 }
 
+base::SharedMemory* GpuMemoryBuffer::GetSharedMemory() {
+  return nullptr;
+}
+
 }  // namespace gfx