This will allow us to more easily create a white box test that sets a
very small initial size for a dynamic buffer.

Bug: angleproject:3082
Change-Id: Ic02bbee83ee8e0f4bfe182e9448c2ce60dea66d5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1667645
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tobin Ehlis <tobine@google.com>