The spec mandates that the instance name of a block determines how the
active uniform name for this field is reported. However, our handling
of this was a bit bugged. We would include the proper prefix on the
compiler-side, but this mangled the hashing, and was also not strictly
needed. We now also expose the instance name, so we can determine the
proper prefix for variable linking on the GL-side of things. This also
is consistent with how we handle other spec issues, where the GL-side
handles the GL-API specific functionality.

This also allows us to fix name hashing of instanced uniform blocks,
which was previously broken because we would hash the full name of the
active uniform, instead of just the field.

BUG=angleproject:1306

Change-Id: I06ace6dbc3f75fdd8129677360dcc142aa89136e
Reviewed-on: https://chromium-review.googlesource.com/326681Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>