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}

modules/video_coding/frame_buffer2.cc

@@ -602,5 +602,9 @@ void FrameBuffer::ClearFramesAndHistory() {
   num_frames_buffered_ = 0;
 }
 
+FrameBuffer::FrameInfo::FrameInfo() = default;
+FrameBuffer::FrameInfo::FrameInfo(FrameInfo&&) = default;
+FrameBuffer::FrameInfo::~FrameInfo() = default;
+
 }  // namespace video_coding
 }  // namespace webrtc