This is a design / refactor task that needs an architecture proposal that makes the thread usage clearer and makes sure ARCore sdk objects all live on one thread (probably the GL thread) and another class is responsible for the communication with Blink.

Probably need to make a "RealARCoreDriver" object that owns ARCore, a GL object (could be the same object) and maybe get rid of ARCoreGLThread entirely and share with GVR (see: https://bugs.chromium.org/p/chromium/issues/detail?id=836553).