Fixed a problem where eglBase.makecurrent() could be called after the context had been released if SurfaceTextureHelper was first created and immedately disconnected. Add the possibility to inject a thread to use instead of creating a new. BUG= webrtc:4993 R=magjed@webrtc.org Review URL: https://codereview.webrtc.org/1384923002 . Cr-Commit-Position: refs/heads/master@{#10174}