We can reduce the amount of iterations we use by using std::vectors
for storing UBO indexes, and resizing them to the max active index.
This allows us to skip inactive ranges. Reduces draw call overhead.

BUG=angleproject:959

Change-Id: I2577e5dbdce0e5ab102ca916eb7f1f35cf03f9ad
Reviewed-on: https://chromium-review.googlesource.com/277287Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>