Fix bugs in HardwareVideoDecoder reinitialization.

Fixes bug where callback is set to null on reinitialization. Also fixes
a race condition where callback can be null in onTextureFrameAvailable.

BUG=webrtc:8124

Review-Url: https://codereview.webrtc.org/3002093002
Cr-Original-Commit-Position: refs/heads/master@{#19493}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6c36dcb324f8dbcefd906ff00c656ca60c9be348
1 file changed