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

cc/resources/shared_bitmap.h

Index: cc/resources/shared_bitmap.h
diff --git a/cc/resources/shared_bitmap.h b/cc/resources/shared_bitmap.h
index 464ac5c6d4c020ed3cab876bc69c50a303843171..f164c44be295bd60fd7bbb987958089a1ca92296 100644
--- a/cc/resources/shared_bitmap.h
+++ b/cc/resources/shared_bitmap.h
@@ -14,6 +14,12 @@
 #include "gpu/command_buffer/common/mailbox.h"
 #include "ui/gfx/geometry/size.h"
 
+namespace base {
+
+class SharedMemory;
+
+}  // namespace base
+
 namespace cc {
 typedef gpu::Mailbox SharedBitmapId;
 
@@ -43,6 +49,8 @@ class CC_EXPORT SharedBitmap {
 
   static SharedBitmapId GenerateId();
 
+  virtual base::SharedMemory* GetSharedMemory() const;
+
  private:
   uint8_t* pixels_;
   SharedBitmapId id_;