This workaround uses UpdateResource instead of staging buffers for
texture data updates. It improves performance for highly dynamic
textures, especially in some benchmarks, eg the turbulenz particle
demo.

BUG=angle:729
BUG=365078

Change-Id: Idd82c27845a772199caef3695111c96735e8843e
Reviewed-on: https://chromium-review.googlesource.com/219864Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>