Refactor TextureStorage11 The CL includes below changes: 1. Change bool isAssociatedImageValid to void verifyAssociatedImageValid since we always required that the validation check should never be false. So ASSERT() is enough. Same to Image11::isAssociatedStorageValid->Image11::verifyAssociatedStorageValid. 2. Remove the unnecessary if checking after ASSERT 3. Use override instead of virtual if the function is virtual and is overriding a virtual function from the base class. BUG=angleproject:2006 Change-Id: I036666ae1ed4bfcaa8cef9e0e9626d375cd81a27 Reviewed-on: https://chromium-review.googlesource.com/480015 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Corentin Wallez <cwallez@chromium.org>