Update from https://crrev.com/311076

base/memory/discardable_shared_memory_unittest.cc

 // Copyright 2014 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/basictypes.h"
 #include "base/memory/discardable_shared_memory.h"
 #include "base/process/process_metrics.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ skipping 269 matching lines @@
 
   // The failed purge attempt should have updated usage time to the correct
   // value.
   EXPECT_EQ(Time::FromDoubleT(5), memory1.last_known_usage());
 
   // Purge should now succeed.
   rv = memory1.Purge(Time::FromDoubleT(7));
   EXPECT_TRUE(rv);
 }
 
+TEST(DiscardableSharedMemoryTest, MappedSize) {
+  const uint32 kDataSize = 1024;
+
+  TestDiscardableSharedMemory memory;
+  bool rv = memory.CreateAndMap(kDataSize);
+  ASSERT_TRUE(rv);
+
+  EXPECT_LE(kDataSize, memory.mapped_size());
+
+  // Mapped size should be 0 after memory segment has been closed.
+  memory.Close();
+  EXPECT_EQ(0u, memory.mapped_size());
+}
+
 }  // namespace
 }  // namespace base