RemoveSwitchFallThrough now correctly records the existence of
declaration and swizzle statements inside switch statements.

BUG=angleproject:2177
TEST=angle_end2end_tests

Change-Id: I1ef83997db7ae510ded002a9568c29272c00c2fe
Reviewed-on: https://chromium-review.googlesource.com/709195Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>