Add bench_playback, for quick profiling of SKR playback.

Add bench_playback, for quick profiling of SKR playback.

It is not completely fair to compare --skr and --noskr numbers.  SKR looks
unfairly good because some optimizations are baked into our SKPs at record
time.  But, at least, by using a kWriteOnly_Mode SkRecorder, we prevent
SkPicturePlayback from compounding that unfairness.  SkRecordDraw must handle
its own playback-time optimizations (quickrejects) on its own.

This code should look suspiciously similar to bench_record.

BUG=skia:2378
R=fmalita@chromium.org, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/233833002

git-svn-id: http://skia.googlecode.com/svn/trunk@14151 2bbb7eff-a529-9590-31e7-b0007b416f81