This is the standard way, if not often used, for application to notify
the driver of window size changes. Chromium uses it to resize when it
is done rendering and swapping so that drivers do not clobber the
backbuffer.
This fixes black flickering appearing when resizing the Chromium
windows with --use-gl=angle.

BUG=angleproject:1281

Change-Id: Ic76f3c3ef453eae07eb59122135290411f86764d
Reviewed-on: https://chromium-review.googlesource.com/322390Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tryjob-Request: Corentin Wallez <cwallez@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>