Enable -Winconsistent-missing-override flag.

webrtc/api/test/fakedtlsidentitystore.h

Index: webrtc/api/test/fakedtlsidentitystore.h
diff --git a/webrtc/api/test/fakedtlsidentitystore.h b/webrtc/api/test/fakedtlsidentitystore.h
index 89c4084d120850ed828d9266c7431db039d67274..c6f5a3c9f76748397ae058be194f36fe220900bd 100644
--- a/webrtc/api/test/fakedtlsidentitystore.h
+++ b/webrtc/api/test/fakedtlsidentitystore.h
@@ -146,7 +146,7 @@ class FakeDtlsIdentityStore : public webrtc::DtlsIdentityStoreInterface,
   const char* get_cert() { return kKeysAndCerts[key_index_].cert_pem; }
 
   // rtc::MessageHandler implementation.
-  void OnMessage(rtc::Message* msg) {
+  void OnMessage(rtc::Message* msg) override {
     MessageData* message_data = static_cast<MessageData*>(msg->pdata);
     rtc::scoped_refptr<webrtc::DtlsIdentityRequestObserver> observer =
         message_data->data();