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

base/memory/ref_counted_memory_unittest.cc

 // Copyright (c) 2011 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 "base/memory/ref_counted_memory.h"
 
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 
@@ skipping 24 matching lines @@
   std::string s("destroy me");
   scoped_refptr<RefCountedMemory> mem = RefCountedString::TakeString(&s);
 
   EXPECT_EQ(0U, s.size());
 
   EXPECT_EQ(10U, mem->size());
   EXPECT_EQ('d', mem->front()[0]);
   EXPECT_EQ('e', mem->front()[1]);
 }
 
+TEST(RefCountedMemoryUnitTest, Equals) {
+  std::string s1("same");
+  scoped_refptr<RefCountedMemory> mem1 = RefCountedString::TakeString(&s1);
+
+  std::vector<unsigned char> d2;
+  d2.push_back('s');
+  d2.push_back('a');
+  d2.push_back('m');
+  d2.push_back('e');
+  scoped_refptr<RefCountedMemory> mem2 = RefCountedBytes::TakeVector(&d2);
+
+  EXPECT_TRUE(mem1->Equals(mem2));
+
+  std::string s3("diff");
+  scoped_refptr<RefCountedMemory> mem3 = RefCountedString::TakeString(&s3);
+
+  EXPECT_FALSE(mem1->Equals(mem3));
+  EXPECT_FALSE(mem2->Equals(mem3));
+}
+
+TEST(RefCountedMemoryUnitTest, EqualsNull) {
+  std::string s("str");
+  scoped_refptr<RefCountedMemory> mem = RefCountedString::TakeString(&s);
+  EXPECT_FALSE(mem->Equals(NULL));
+}
+
 }  //  namespace base