We would end up with a large reserved space even though the
allocation failed. Insead set the reserved space size after
the allocation succedes.
This was showing up as angle_end2end_tests failures on
Windows 7 due to display reuse and buffer allocation.
Bug: chromium:944454
Change-Id: Idb3bd530fe7b9cc2fce9a579787684e632b1a637
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1534684Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
