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Also refactor the fake draw_fn implementation. This is to prepare for
adding a vulkan draw_fn implementation.

Split draw_fn implementation into:
allocator.cc/h: Controls functor data lifetime
context_manager: Effectively global. Responsible for owning the surface
                 and EGL context. Calls sync/draw/context_destroyed on
                 functor and responsible for owning the "impl reference"
                 to functor data.

context_manager uses EGL bindings from ui/gl, but nothing else
to avoid conflicting with chromium side implementations, and to avoid
initializing a TaskRunner on render thread. Only GLES call is
glReadPixels after draw, which relies on chromium implementation not
releasing its bindings after draw.

Refactor and simplify the java side by explicitly adding a thread to
post tasks and a WaitableEvent; this avoids saving state and using
a Lock object.

Cq-Include-Trybots: luci.chromium.try:gpu-fyi-try-android-m-nexus-5x-64
Bug: 1141687
Change-Id: I71752b31f401fdb277062fe1347dfa826a20bb81
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587238
Auto-Submit: Bo <boliu@chromium.org>
Commit-Queue: Jonathan Backer <backer@chromium.org>
Reviewed-by: Jonathan Backer <backer@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837094}