CameraPreviewSurfaceTexture: fix camera exit crash issue

Signed-off-by: Wayne Wolf <wayne ron wu ## gmail>
CameraPreviewImageButton: emulate hangout

skeleton code cloned from CameraPreviewSurfaceTexture.

Signed-off-by: Wayne Wolf <wayne ron wu ## gmail>
CameraPreviewImageButton: convert preview image to rgb, set it to ImageButton

Signed-off-by: Wayne Wolf <wayne ron wu ## gmail>