This avoid unnecessary binary bloat from STL default constructors
and assignment operators.

BUG=angle:466,697

Change-Id: I679e524d3e3dbd0d3866fc30a5a01967d8769249
Reviewed-on: https://chromium-review.googlesource.com/208356Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: bratell at Opera <bratell@opera.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>