Re-land fixes memory leak and adds inline to a few more methods.

This optimized vector keeps an initial fixed size storage but has
unbounded growth like a normal std::vector. It operates like a
FixedVector initially but then switches the storage to an allocated
pool when the element count exceeds the array limit.

This gives fast performance in the small case since no dynamic
allocation is needed. It also handles the "slow" big case.

Bug: angleproject:2763
Change-Id: Ib3cc7b652a14ed346528bf15820023ab0b5317ce
Reviewed-on: https://chromium-review.googlesource.com/1233453
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>