Add top-level dirty bits for texture and samplers. These will have to be fleshed out in the back-ends. Also currently uses a single bit for all the bindings, and we can extend this to more fine-grained updates in the future. This patch implements top-level updates for texture completeness. Sampler completeness caches are removed from the Texture class, and replaced by a cache in the gl::State class. The State class also keeps a channel binding to the bound textures so it can be notified when textures might change from complete <-> incomplete. In future CLs we skip updating back-ends if texture state doesn't change. BUG=angleproject:1387 Change-Id: If580b4851303c86f3240e62891f5f6047eefb6a2 Reviewed-on: https://chromium-review.googlesource.com/648053 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>