Rename some cricket::VideoFrame methods, to align with webrtc::VideoFrame.

webrtc/api/objc/RTCVideoFrame.mm

Index: webrtc/api/objc/RTCVideoFrame.mm
diff --git a/webrtc/api/objc/RTCVideoFrame.mm b/webrtc/api/objc/RTCVideoFrame.mm
index 95f4ac82bfe3fd2350461f49842bcc2c0ca92cec..6a4b1aab514416be0d6cca60c888d0fe8b2a7a45 100644
--- a/webrtc/api/objc/RTCVideoFrame.mm
+++ b/webrtc/api/objc/RTCVideoFrame.mm
@@ -92,10 +92,10 @@
   if (!_i420Buffer) {
     if (_videoFrame->GetNativeHandle()) {
       // Convert to I420.
-      _i420Buffer = _videoFrame->GetVideoFrameBuffer()->NativeToI420Buffer();
+      _i420Buffer = _videoFrame->video_frame_buffer()->NativeToI420Buffer();
     } else {
       // Should already be I420.
-      _i420Buffer = _videoFrame->GetVideoFrameBuffer();
+      _i420Buffer = _videoFrame->video_frame_buffer();
     }
   }
 }