Add 5-argument wrapper WebRtcVideoFrame::InitToBlack

For some reason, inheriting it doesn't work.

BUG=webrtc:5426
R=perkj@webrtc.org

Review URL: https://codereview.webrtc.org/1602543003 .

Cr-Commit-Position: refs/heads/master@{#11290}

talk/media/webrtc/webrtcvideoframe.h

@@ -73,6 +73,9 @@ class WebRtcVideoFrame : public VideoFrame {
   }
 
   bool InitToBlack(int w, int h, int64_t time_stamp_ns) override;
+  // Needed to inherit the InitToBlack wrapper method with 5
+  // arguments.
+  using VideoFrame::InitToBlack;
 
   // From base class VideoFrame.
   bool Reset(uint32_t format,