[androidkit] implement ThreadedSurface backed by WindowSurface

This moves ownership of the SkSurface to ThreadedSurface::fWindowSurface.

When we pass a Message to the SurfaceThread, we will include  a pointer to ThreadedSurface.fWindowSurface so we can call:
getCanvas() to draw the SkPicture
WindowSurface's constructor so it can hold the WindowContext made during the init

To reference WindowSurface in SurfaceThread, we need to make a header for Surface.cpp (added in this cl)

Change-Id: I8c67223eee301a1b6e0d05934e1f8597cf70bc64
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/404918
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
6 files changed