If TextureImpl sets a local dirty bit and signals gl::Texture of it, the
dirtyness is not propogated to context.  This can result in draw calls
with textures that are not synchronized

BUG=949985

Change-Id: I9baf82c96598265a6a4850f1fd48e213b5e98ab5
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1556699
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>