GLRenderer: only disable shared images on Android

Shared images are necessary to implement WebGPU on Mac, make sure they
are disabled only on the platform that requires them disabled.

BUG=chromium:900963
BUG=chromium:877147

Change-Id: Ie588d40e5e2d38b57037422c4dd04213617f20eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1579979
Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653518}
1 file changed