Lowp overlay, hardlight stages

Before:

    micros   	bench
   7669.09 ?	blendmode_rect_HardLight	8888
   8707.13 ?	blendmode_rect_Overlay	8888


After:

    micros   	bench
   6679.60 ?	blendmode_rect_HardLight	8888
   6789.57 ?	blendmode_rect_Overlay	8888

Change-Id: I52f389253fa07dafe18e572af550af7387264a16
Reviewed-on: https://skia-review.googlesource.com/34280
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@google.com>
4 files changed