Since querying the internal format of an attachment might need ot look
at the RenderTarget for some back-ends, or otherwise flush attachment
changes, we should call syncState internally. This means that we can't
mark these queries as const.

Bug: angleproject:2372
Change-Id: I9bfb43a472bcd7dfdd6ea7fab4751d494e1126bb
Reviewed-on: https://chromium-review.googlesource.com/948784Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>