Improve usage of window rectangles

* Skips non-AA diff rect elements and replaces them with window
  rectangles.
* Places window rectangles in the interiors of antialiased diff rects.
* Arranges two overlapping window rectangles in a plus shape inside of
  diff rounded rects.
* Enables window rectangles when clearing and generating clip masks.

GTX 960 perf result (with vs. without window rectangles):

                              glinst4                msaa16                 gpu
keymobi_pinterest.skp         0.48 -> 0.17 [ 35%]    2.77 -> 1.49 [ 54%]    0.22 -> 0.16 [ 70%]
keymobi_digg_com.skp          0.42 -> 0.23 [ 55%]    2.34 -> 1.08 [ 46%]    0.25 -> 0.21 [ 83%]
desk_jsfiddlebigcar.skp       0.28 -> 0.16 [ 59%]    1.70 -> 0.96 [ 57%]    0.19 -> 0.14 [ 70%]
top25desk_wordpress.skp       0.45 -> 0.18 [ 40%]    2.78 -> 1.53 [ 55%]    0.21 -> 0.19 [ 94%]
top25desk_weather_com.skp     2.01 -> 1.93 [ 96%]    23.5 -> 2.54 [ 11%]    1.90 -> 1.68 [ 88%]
keymobi_blogger.skp           0.57 -> 0.37 [ 65%]    2.87 -> 1.54 [ 54%]    0.43 -> 0.33 [ 77%]
keymobi_linkedin.skp          0.32 -> 0.17 [ 51%]    1.93 -> 1.04 [ 54%]    0.17 -> 0.15 [ 91%]
keymobi_bing_com_search_...   0.29 -> 0.25 [ 83%]    1.85 -> 1.23 [ 66%]    0.50 -> 0.24 [ 48%]
keymobi_theverge_com_201...   1.00 -> 0.67 [ 68%]    9.46 -> 3.84 [ 41%]    0.72 -> 0.65 [ 90%]
keymobi_sfgate_com_.skp       1.56 -> 1.13 [ 72%]    4.49 -> 2.86 [ 64%]    1.54 -> 1.11 [ 72%]
...
GEOMEAN (All 79 blink skps)   1.04 -> 0.90 [ 86%]    4.22 -> 2.81 [ 67%]    0.95 -> 0.89 [ 94%]

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2289363005

Committed: https://skia.googlesource.com/skia/+/db42be9a326c747ff92ed1da8c3536c5b3e8e22b
Review-Url: https://codereview.chromium.org/2289363005

0 files changed, 0 insertions, 0 deletions