WebRTC: Fix and enable -Woverloaded-virtual warnings.

webrtc/api/peerconnectioninterface_unittest.cc

 /*
  *  Copyright 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 417 matching lines @@
   }
 
   MOCK_METHOD0(OnChanged, void());
 
  private:
   NotifierInterface* notifier_;
 };
 
 class MockPeerConnectionObserver : public PeerConnectionObserver {
  public:
+  // We need these using declarations because there are two versions of each of
+  // the below methods and we only override one of them.
+  // TODO(deadbeef): Remove once there's only one version of the methods.
+  using PeerConnectionObserver::OnAddStream;
+  using PeerConnectionObserver::OnRemoveStream;
+  using PeerConnectionObserver::OnDataChannel;
+
   MockPeerConnectionObserver() : remote_streams_(StreamCollection::Create()) {}
   virtual ~MockPeerConnectionObserver() {
   }
   void SetPeerConnectionInterface(PeerConnectionInterface* pc) {
     pc_ = pc;
     if (pc) {
       state_ = pc_->signaling_state();
     }
   }
   void OnSignalingChange(
@@ skipping 2444 matching lines @@
   FakeConstraints updated_answer_c;
   answer_c.SetMandatoryReceiveAudio(false);
   answer_c.SetMandatoryReceiveVideo(false);
 
   cricket::MediaSessionOptions updated_answer_options;
   EXPECT_TRUE(
       ParseConstraintsForAnswer(&updated_answer_c, &updated_answer_options));
   EXPECT_TRUE(updated_answer_options.has_audio());
   EXPECT_TRUE(updated_answer_options.has_video());
 }