Standardize usage of virtual/override/final specifiers in base/.

base/files/memory_mapped_file_unittest.cc

Index: base/files/memory_mapped_file_unittest.cc
diff --git a/base/files/memory_mapped_file_unittest.cc b/base/files/memory_mapped_file_unittest.cc
index 36999bfba92a2623c0631285c60d5321c124d73d..d0833b5cc9a24459857a356b5a7f013ca1ba8c49 100644
--- a/base/files/memory_mapped_file_unittest.cc
+++ b/base/files/memory_mapped_file_unittest.cc
@@ -29,12 +29,12 @@ bool CheckBufferContents(const uint8* data, size_t size, size_t offset) {
 
 class MemoryMappedFileTest : public PlatformTest {
  protected:
-  virtual void SetUp() override {
+  void SetUp() override {
     PlatformTest::SetUp();
     CreateTemporaryFile(&temp_file_path_);
   }
 
-  virtual void TearDown() { EXPECT_TRUE(DeleteFile(temp_file_path_, false)); }
+  void TearDown() override { EXPECT_TRUE(DeleteFile(temp_file_path_, false)); }
 
   void CreateTemporaryTestFile(size_t size) {
     File file(temp_file_path_,