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

base/memory/ref_counted_memory.cc

Index: base/memory/ref_counted_memory.cc
diff --git a/base/memory/ref_counted_memory.cc b/base/memory/ref_counted_memory.cc
index 9bcde32b60ec77bb1bc88721256f59d0e3f9f67b..b048a6e0d8d2352936e9cb995479058c13f17ba4 100644
--- a/base/memory/ref_counted_memory.cc
+++ b/base/memory/ref_counted_memory.cc
@@ -8,6 +8,13 @@
 
 namespace base {
 
+bool RefCountedMemory::Equals(
+    const scoped_refptr<RefCountedMemory>& other) const {
+  return other.get() &&
+         size() == other->size() &&
+         (memcmp(front(), other->front(), size()) == 0);
+}
+
 RefCountedMemory::RefCountedMemory() {}
 
 RefCountedMemory::~RefCountedMemory() {}