Simplify difference and exclusion.

We can fold through some math in these two modes.

$ out/ok bench:samples=100 rp filter:search="Difference|Exclusion" serial

Before:
    [blendmode_rect_Exclusion]  4.94ms  @0  6.13ms  @99 6.25ms  @100
    [blendmode_mask_Exclusion]  10.9ms  @0  12.8ms  @99 12.9ms  @100
    [blendmode_rect_Difference] 5.56ms  @0  6.79ms  @99 6.8ms   @100
    [blendmode_mask_Difference] 11.4ms  @0  13.8ms  @99 14.1ms  @100

After:
    [blendmode_rect_Exclusion]  3.5ms   @0  4.12ms  @99 4.59ms  @100
    [blendmode_mask_Exclusion]  9.27ms  @0  11.2ms  @99 11.6ms  @100
    [blendmode_rect_Difference] 5.37ms  @0  6.58ms  @99 6.6ms   @100
    [blendmode_mask_Difference] 11ms    @0  12.1ms  @99 12.6ms  @100

Change-Id: I03f32368244d4f979cfee83723fd78dfbc7d5fc1
Reviewed-on: https://skia-review.googlesource.com/33980
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>

0 files changed, 0 insertions, 0 deletions