Compare all uniform data to the values currently stored in the uniform and
only mark the uniform as dirty if the data is new.  This saves lots of
buffer map calls when the same data is set on a uniform many times.

BUG=260069

Change-Id: Ic4df8a276a81b074211712ff50e5cc4d0d9bb612
Reviewed-on: https://chromium-review.googlesource.com/199346Reviewed-by: Nicolas Capens <nicolascapens@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>