Remove call sites of RegisterUMAObserver.

RegisterUMAObserver is soon to be deprecated in PeerConnectionInterface
in WebRTC.

Bug: None
Change-Id: Iad9fe987ee9dcd1512c332a7084e2d1ae5cc4774
Reviewed-on: https://chromium-review.googlesource.com/1141173
Commit-Queue: Qingsi Wang <qingsi@google.com>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576160}

content/renderer/media/webrtc/mock_peer_connection_impl.cc

@@ -489,11 +489,6 @@ bool MockPeerConnectionImpl::AddIceCandidate(
   return candidate->ToString(&ice_sdp_);
 }
 
-void MockPeerConnectionImpl::RegisterUMAObserver(
-    webrtc::UMAObserver* observer) {
-  NOTIMPLEMENTED();
-}
-
 webrtc::RTCError MockPeerConnectionImpl::SetBitrate(
     const webrtc::BitrateSettings& bitrate) {
   NOTIMPLEMENTED();

content/renderer/media/webrtc/mock_peer_connection_impl.h

@@ -216,7 +216,6 @@ class MockPeerConnectionImpl : public webrtc::PeerConnectionInterface {
   bool SetConfiguration(const RTCConfiguration& configuration,
                         webrtc::RTCError* error) override;
   bool AddIceCandidate(const webrtc::IceCandidateInterface* candidate) override;
-  void RegisterUMAObserver(webrtc::UMAObserver* observer) override;
 
   webrtc::RTCError SetBitrate(const webrtc::BitrateSettings& bitrate) override;