Enable -Winconsistent-missing-override flag.

The problem with gmock is worked around by commenting out any other override declarations in classes using gmock.

NOPRESUBMIT=True
BUG=webrtc:3970

Review-Url: https://codereview.webrtc.org/1921653002
Cr-Commit-Position: refs/heads/master@{#12563}
diff --git a/webrtc/api/test/fakeaudiocapturemodule_unittest.cc b/webrtc/api/test/fakeaudiocapturemodule_unittest.cc
index 8ac1acc..d0dcd85 100644
--- a/webrtc/api/test/fakeaudiocapturemodule_unittest.cc
+++ b/webrtc/api/test/fakeaudiocapturemodule_unittest.cc
@@ -31,7 +31,7 @@
     memset(rec_buffer_, 0, sizeof(rec_buffer_));
   }
 
-  virtual void SetUp() {
+  void SetUp() override {
     fake_audio_capture_module_ = FakeAudioCaptureModule::Create();
     EXPECT_TRUE(fake_audio_capture_module_.get() != NULL);
   }