Add a bench for comparing complex clip strategies

Clip consisting of a union of |n| circles.

Comparing mask (2x saveLayer + srcIn) vs. clipPath approaches.

MBP numbers:

! -> high variance, ? -> moderate variance
    micros   	bench
    233.05 !	clip_strategy_mask_100	gl
    207.61 !	clip_strategy_mask_10	gl
    210.41 ?	clip_strategy_mask_5	gl
    219.10 ?	clip_strategy_mask_1	gl
    115.56 ?	clip_strategy_path_100	gl
    113.29 !	clip_strategy_path_10	gl
    102.36 ?	clip_strategy_path_5	gl
      6.37 ?	clip_strategy_path_1	gl

    361.06 !	clip_strategy_mask_100	8888
    328.97 !	clip_strategy_mask_10	8888
    316.72 !	clip_strategy_mask_5	8888
    325.84 !	clip_strategy_mask_1	8888
    368.54 !	clip_strategy_path_100	8888
    306.99 !	clip_strategy_path_10	8888
    298.71 !	clip_strategy_path_5	8888
    191.00 !	clip_strategy_path_1	8888

TBR=

Change-Id: I945c12e2e35b9847af06342473e56272e2041e21
Reviewed-on: https://skia-review.googlesource.com/72521
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
2 files changed