Update from https://crrev.com/311076

base/memory/discardable_shared_memory_unittest.cc

Index: base/memory/discardable_shared_memory_unittest.cc
diff --git a/base/memory/discardable_shared_memory_unittest.cc b/base/memory/discardable_shared_memory_unittest.cc
index 90441e1f35f47f8ab4db8eb79d5fe8998bf5e12f..896263df60927b6df3aaba8a3628f5ea5a203f81 100644
--- a/base/memory/discardable_shared_memory_unittest.cc
+++ b/base/memory/discardable_shared_memory_unittest.cc
@@ -287,5 +287,19 @@ TEST(DiscardableSharedMemoryTest, LockAndUnlockRange) {
   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