Store un-linked shader attributes in ProgramBinary. Our caching of compiled vertex shaders according to their input signature needs a consistent input signature to match up shaders. Since the linking step currently shuffles attributes according to API specified locations we need a separate list. BUG=angle:560 Change-Id: Icc4d5df1d37ae895d5c882b86e60f05b5c268461 Reviewed-on: https://chromium-review.googlesource.com/185193 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>