Good for implementing stacks of fixed size (in the pop operation).

+ fix an issue where push_back() only allows adding up to max_size() - 1
elements.

BUG=angleproject:2306

Change-Id: I99b3c8416055f069fa563b684c102fd6aec116bc
Reviewed-on: https://chromium-review.googlesource.com/1000031Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Lingfeng Yang <lfy@google.com>