Remove kSkipFrame usage.

Since padding is no longer sent on Encoded() callbacks, dummy callbacks
aren't required to generate padding. This skip-frame behavior can then
be removed to get rid of dummy callbacks though nothing was encoded. As
frames don't have to be generated for frames that don't have to be sent
we skip encoding frames that aren't intended to be sent either, reducing
CPU load.

BUG=
R=mflodman@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1369923005 .

Cr-Commit-Position: refs/heads/master@{#10181}

webrtc/modules/video_coding/main/source/encoded_frame.cc

@@ -233,11 +233,9 @@ webrtc::FrameType VCMEncodedFrame::ConvertFrameType(VideoFrameType frameType)
       return  kVideoFrameKey;
     case kDeltaFrame:
       return kVideoFrameDelta;
-    case kSkipFrame:
-      return kFrameEmpty;
-    default:
-      return kVideoFrameDelta;
   }
+  // Bogus default return value.
+  return kVideoFrameDelta;
 }
 
 VideoFrameType VCMEncodedFrame::ConvertFrameType(webrtc::FrameType frame_type) {