[StateManagerGL] Add asserts to each mFunctions->get*() call Will enable pinpointing where the assert that is going off in crbug.com/1434317 is coming from. Can revert if desired once we have needed info. Note: All of these gets are called only from syncFromNativeContext() or functions that are called by that function, so adding these asserts shouldn't result in any new crashes beyond those that would already be generated via the assert at the end of syncFromNativeContext(). Bug: chromium:1434317 Change-Id: I3dfa12f631bfbbb567d6043cc467d0ddfa8911e5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4451907 Auto-Submit: Colin Blundell <blundell@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>