We were missing a dependency insertion between the Framebuffer and
its attachments, only during clear operations. Also renames a few
methods to make them more consistent.

Bug: angleproject:2264
Change-Id: Ic3af5b34b6de900ea2cc1b765f8d3d69f7f9a131
Reviewed-on: https://chromium-review.googlesource.com/891985Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>