Drop any pending texture frame when SurfaceTextureHelper.startListening()
is called because the frame might be from the previous
startListening()/stopListening() capture session. This typically happens
when switching between the front/back camera, and an old frame will get
incorrect rotation and mirroring because of the front/back camera
mismatch.
Dropping the frame in SurfaceTextureHelper also removes the need for
the |dropNextFrame| logic in VideoCapturerAndroid.
R=perkj@webrtc.org
Review URL: https://codereview.webrtc.org/2002963002 .
Cr-Commit-Position: refs/heads/master@{#12849}
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