This completes the work for the simple texture sample.

Bug: angleproject:2167
Change-Id: I47c6794fa7cd59e295a98623d9ce8879ea1d3298
Reviewed-on: https://chromium-review.googlesource.com/952566Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>