Currently, VideoCapturerAndroid owns a dedicated tread, and
SurfaceTextureHelper get this thread passed in the ctor. In
VideoCapturerAndroid.dispose(), ownership of the thread is passed to
SurfaceTextureHelper so that we can return directly instead of waiting
for the last frame to return.
This CL makes the SurfaceTextureHelper own the thread the whole time
instead, and VideoCapturerAndroid calls getHandler() to get it instead.
BUG=webrtc:5519
Review URL: https://codereview.webrtc.org/1738123002
Cr-Commit-Position: refs/heads/master@{#11790}
9e69dfdfd5