Update bench to be able to preprocess skps

This allows benchmarking of optimization improvements and plumbs in the purging API. The purging is necessary so we don't magically get faster because the saveLayers are always pre-generated.

R=jvanverth@google.com, reed@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/233663002

git-svn-id: http://skia.googlecode.com/svn/trunk@14154 2bbb7eff-a529-9590-31e7-b0007b416f81
9 files changed