It appears this optimization causing Manhattan performance regression on
pixel4 with QualComm GPU. It does have a measurable performance
improvement on S20+ that has ARM GPU. This disables this optimization
for QualComm but still leaves it enabled on other GPUs.

Bug: b/166475273
Change-Id: I9c9cd55ab169463fc8cc16d7d917be660cb2f363
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2441667Reviewed-by: Mohan Maiya <m.maiya@samsung.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Charlie Lao <cclao@google.com>