This reduces preferredLargeHeapBlockSize from the default
value of 256 MB to 4 MB, which reduces the initial block
size from 32 MB to 512 KB.

4 MB is the same size as used by Chromium and Skia. It seems
to be a good compromise of not wasting unused allocated space
and not making too many small allocations.

This change is limited to non-Qualcomm GPUs as a number of
tests are failing on Qualcomm after this change and the
initial investigation indicates a potential driver bug. See
http://anglebug.com/4995 for more details.

Bug: chromium:1122718
Bug: fuchsia:58959
Change-Id: Ifdaf863ef38e72098a04ee57dec46ee71cab6ac3
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2376891Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: David Reveman <reveman@chromium.org>