Move VideoFrame and related declarations to webrtc/api/video.

webrtc/common_video/video_frame_buffer.cc

Index: webrtc/common_video/video_frame_buffer.cc
diff --git a/webrtc/common_video/video_frame_buffer.cc b/webrtc/common_video/video_frame_buffer.cc
index 1ee97531b07aac91a9b169a08ddbba3c9b5e1477..b55818d73af189073a76cb0ccfb66e709db44610 100644
--- a/webrtc/common_video/video_frame_buffer.cc
+++ b/webrtc/common_video/video_frame_buffer.cc
@@ -32,8 +32,6 @@ int I420DataSize(int height, int stride_y, int stride_u, int stride_v) {
 
 }  // namespace
 
-VideoFrameBuffer::~VideoFrameBuffer() {}
-
 I420Buffer::I420Buffer(int width, int height)
     : I420Buffer(width, height, width, (width + 1) / 2, (width + 1) / 2) {
 }