This cleans up a few places where we were initializing the dynamic
buffers.

Bug: angleproject:2729
Change-Id: I0c9a61c62ef4d0eb865abc0011f7086d6e2acef6
Reviewed-on: https://chromium-review.googlesource.com/1142297
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Frank Henigman <fjhenigman@chromium.org>