Don't re-randomize picture_id/tl0_pic_idx when re-initializing internal encoders.

webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc

Index: webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc
diff --git a/webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc b/webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc
index e2246b06ad3acfd8205265aa09b1b57012e66740..8301cc9f1dde1ef020702d8093adb4ec8fa56018 100644
--- a/webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc
+++ b/webrtc/modules/video_coding/codecs/vp8/default_temporal_layers.cc
@@ -194,6 +194,10 @@ int DefaultTemporalLayers::CurrentLayerId() const {
   return temporal_ids_[pattern_idx_ % temporal_ids_.size()];
 }
 
+uint8_t DefaultTemporalLayers::Tl0PicIdx() const {
+  return tl0_pic_idx_;

[brandtr, 2017/04/20 08:59:11]

If the first frame after a reinit always is a tl0 frame (it should be, since
it's a key frame), then |tl0_pic_idx_| will be incremented here:
https://cs.chromium.org/chromium/src/third_party/webrtc/modules/video_coding/....

So we should return and initialize with the current value, not the current+1
value.

Please help me verify that I don't introduce an off-by-one error here :)

[stefan-webrtc, 2017/04/20 09:28:09]

Maybe we can add a test in vp8_impl_unittests.cc to verify this?

+}
+
 std::vector<uint32_t> DefaultTemporalLayers::OnRatesUpdated(
     int bitrate_kbps,
     int max_bitrate_kbps,