Clean up state query methods. Consolidate a lot of the code duplication in GetIntegerv, GetFloatv, GetBooleanv and GetInteger64v. BUG=angle:540 Change-Id: I7b4a5803ea76e5eeb0ebf25c5caadec4c647b485 Reviewed-on: https://chromium-review.googlesource.com/180971 Commit-Queue: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Nicolas Capens <nicolascapens@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>