In both Texture and State, track when all images/textures are
initailized so that State::clearUnclearedActiveTextures can early-exit.
Improves performance on the WebGL Aquarium by 26% (23->29 FPS) with 30000
fish.
BUG=angleproject:2188
Change-Id: Ie2860a81d7be19ee87262325d8cf27bde43f80b8
Reviewed-on: https://chromium-review.googlesource.com/782339
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
