Changing RtpSenderInterface::GetParameters overrides to const.

The RtpSenderInterface::GetParameters() method was mistakenly not
declared as const. This has been fixed in webrtc.
This change aligns overrides to declare the const method as well.

Bug: webrtc:10251
TBR: orphis@chromium.org
Change-Id: I3bfb87f11e84d14c7bae9c3b1e6ec2b303aabb56
Reviewed-on: https://chromium-review.googlesource.com/c/1479411
Commit-Queue: Amit Hilbuch <amithi@chromium.org>
Reviewed-by: Steve Anton <steveanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634749}

content/renderer/media/webrtc/mock_peer_connection_impl.cc

@@ -154,7 +154,7 @@ std::vector<webrtc::RtpEncodingParameters> FakeRtpSender::init_send_encodings()
   return {};
 }
 
-webrtc::RtpParameters FakeRtpSender::GetParameters() {
+webrtc::RtpParameters FakeRtpSender::GetParameters() const {
   NOTIMPLEMENTED();
   return webrtc::RtpParameters();
 }

content/renderer/media/webrtc/mock_peer_connection_impl.h

@@ -38,7 +38,7 @@ class FakeRtpSender : public webrtc::RtpSenderInterface {
   std::vector<std::string> stream_ids() const override;
   std::vector<webrtc::RtpEncodingParameters> init_send_encodings()
       const override;
-  webrtc::RtpParameters GetParameters() override;
+  webrtc::RtpParameters GetParameters() const override;
   webrtc::RTCError SetParameters(
       const webrtc::RtpParameters& parameters) override;
   rtc::scoped_refptr<webrtc::DtmfSenderInterface> GetDtmfSender()