gpu, cmaa: Don't blend large L shape because it would be the intended shape with high probability.

Large L shape is as follows;
_ _         |     |         _ _
  X|       X|     |X       |X
   |     ¯¯¯¯     ¯¯¯¯     |

We don't want to blur the corner of a rectangle.

BUG=535198
TEST=Run a WebGL app with Chrome started with "--enable-cmaa-shaders"
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2109603003
Cr-Commit-Position: refs/heads/master@{#402796}
1 file changed