GLES1 has at least two places where all texture objects
can carry more state:

- Crop rectangle, used with glDrawTex
- Generate mipmap parameter, which lets the user
  auto-generate mipmaps for textures from a texture
  parameter

This CL adds them to the Texture / TextureState classes.

BUG=angleproject:2306

Change-Id: Ia43882d36f166b49a09434e77f8c288478e2a454
Reviewed-on: https://chromium-review.googlesource.com/909579Reviewed-by: Lingfeng Yang <lfy@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Lingfeng Yang <lfy@google.com>