* Add back launch screen view until first frame on iOS
* improvements
* Move callback plumbing from ios surfaces to the gpu rasterizer. Didn’t wire java JNI yet.
* Android JNI
* Fix ios reference count and let android engine manage a view on top with launch screen
* Hook up Android activity and view
* review notes
* review notes
* Move thread switching upstream. Use weak references for callbacks.
* Some clean up
The GPUSurfaceGL holds references to Skia objects that may own GL objects.
If the GL objects are destructed on the GPU thread after the EGL context has been
dropped, then the GL delete calls will not take effect.
