Fix chromium warnings for SdpVideoFormat.

Bug: webrtc:163
Change-Id: I29ad3c00116692f047456df7721ba636bbb2ca89
Reviewed-on: https://webrtc-review.googlesource.com/64723
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22618}
diff --git a/modules/video_coding/include/video_coding_defines.h b/modules/video_coding/include/video_coding_defines.h
index e000bc6..ea3e3ec 100644
--- a/modules/video_coding/include/video_coding_defines.h
+++ b/modules/video_coding/include/video_coding_defines.h
@@ -73,12 +73,10 @@
                                 rtc::Optional<uint8_t> qp,
                                 VideoContentType content_type) = 0;
 
-  virtual int32_t ReceivedDecodedReferenceFrame(const uint64_t pictureId) {
-    return -1;
-  }
+  virtual int32_t ReceivedDecodedReferenceFrame(const uint64_t pictureId);
   // Called when the current receive codec changes.
-  virtual void OnIncomingPayloadType(int payload_type) {}
-  virtual void OnDecoderImplementationName(const char* implementation_name) {}
+  virtual void OnIncomingPayloadType(int payload_type);
+  virtual void OnDecoderImplementationName(const char* implementation_name);
 
  protected:
   virtual ~VCMReceiveCallback() {}