GitLab

In preparation for GpuFence synchronization, track GVR acquire/submit
times and report JavaScript waitForPreviousRender times back to
VrShellGl via Mojo.

Refactor waiting for previous transfer and render, using helper
functions to unclutter submitFrame.

Wait for previous transfer is only used for the Android surface path,
move it there.

Wait for previous render now support different choices for the
execution point, including NEVER for the OpenVR path. The BEFORE_BITMAP
choice is not yet active, it's intended for use with GpuFence-separated
frames. It does work for the current render path too, but IIRC is a bit
slower there due to less parallelism.

BUG=761432

Change-Id: I9d24d6e0a133ad76cfda4f40c2bba84ffd7363ef
Reviewed-on: https://chromium-review.googlesource.com/802756Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Bill Orr <billorr@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521735}