Avoid sending notifications when the bitmap data in history has not changed

base/memory/ref_counted_memory.h

Index: base/memory/ref_counted_memory.h
diff --git a/base/memory/ref_counted_memory.h b/base/memory/ref_counted_memory.h
index 9edcd6fdc94d7f358596dcc2a39153a38d7e0b0f..b86de578dd036a4eea2092f38135a2076e390d07 100644
--- a/base/memory/ref_counted_memory.h
+++ b/base/memory/ref_counted_memory.h
@@ -27,6 +27,9 @@ class BASE_EXPORT RefCountedMemory
   // Size of the memory pointed to.
   virtual size_t size() const = 0;
 
+  // Returns true if |other| is byte for byte equal.
+  bool Equals(const RefCountedMemory* other) const;
+
  protected:
   friend class base::RefCountedThreadSafe<RefCountedMemory>;
   RefCountedMemory();