Invalidate completeness caches when enabling extensions. Enabling extensions can cause framebuffers and textures to go from incomplete to complete. No functional changes from the API surface. BUG=angleproject:1523 BUG=angleproject:1958 Change-Id: Iff686e1c292f6cf4921d6fffd7eb98bedaba828b Reviewed-on: https://chromium-review.googlesource.com/468410 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>