Delete VideoFrame default constructor, and IsZeroSize method.

webrtc/modules/video_coding/generic_encoder.cc

Index: webrtc/modules/video_coding/generic_encoder.cc
diff --git a/webrtc/modules/video_coding/generic_encoder.cc b/webrtc/modules/video_coding/generic_encoder.cc
index 75bdc7c4f39c534b62270b537d23e6bb43559d8a..1786e72ea26009207fe40a94b66e77b9d05099b2 100644
--- a/webrtc/modules/video_coding/generic_encoder.cc
+++ b/webrtc/modules/video_coding/generic_encoder.cc
@@ -123,8 +123,14 @@ int32_t VCMGenericEncoder::SetPeriodicKeyFrames(bool enable) {
 int32_t VCMGenericEncoder::RequestFrame(
     const std::vector<FrameType>& frame_types) {
   RTC_DCHECK_RUNS_SERIALIZED(&race_checker_);
-  VideoFrame image;
-  return encoder_->Encode(image, NULL, &frame_types);
+
+  // TODO(nisse): Used only with internal source. Delete as soon as
+  // that feature is removed. The only implementation I've been able
+  // to find ignores what's in the frame.
+  return encoder_->Encode(VideoFrame(I420Buffer::Create(1, 1),

[magjed_webrtc, 2016/11/30 16:23:56]

This looks very strange. What's the purpose here?

[nisse-webrtc, 2016/11/30 16:36:00]

The way I understand it, when the "internal source" hack is used, normal video
frames are never sent to the Encode method, because the encoder is hooked up
directly to the camera in some way, perhaps the source produces encoded frames
directly.

But since that's the only way to get the key frame request signal across the
encoder interface, the encoder object for that case implements an Encode method
which examines the frame_type argument, and ignores the frame.

This was the smallest change to make that ugly hack still work (it used to pass
a VideoFrame where video_frame_buffer() is null)). The right way would probably
be to add an encoder method specifically for keyframe request signalling. But
that's a refactoring unrelated to this cl.

[magjed_webrtc, 2016/12/01 11:46:38]

Acknowledged.

+                                     kVideoRotation_0, 0),
+                          NULL, &frame_types);
+  return 0;

[nisse-webrtc, 2016/11/30 16:36:00]

But this extra return statement looks very wrong.

 }
 
 bool VCMGenericEncoder::InternalSource() const {