Harden gpu::SizedResult against overflow

Use CheckedNumerics to prevent silent uint32_t overflow.

Bug: 905336, 905459
Change-Id: Ie518def9063143ef2393be566419a209f68f0dce
Reviewed-on: https://chromium-review.googlesource.com/c/1336083
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Abhishek Arya <inferno@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608184}