Clean up the includes and imports for this module as well.

BUG: angleproject:2475
TEST: Built cast_runner, web_runner
Change-Id: Id283c265a4ec9d2ca74e3a0132e82f051b8864f6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1579219Reviewed-by: Michael Spang <spang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>