Add script to rebaseline benches from codereview trybot results

Add script to rebaseline benches from codereview trybot results

This script is designed to be used by the RecreateSKPs bot.  Eventually, the bot will:
1. Generate new SKPs
2. Upload the new SKPs to a subdirectory with an ID or generation number.
3. Change Skia to use the new SKPs:
    a. Create and upload a Skia CL which changes the "current SKP generation" file to point to the new SKPs
    b. Launch Perf trybots on that CL.
    c. Call this script every 5 minutes until it successfully creates new baselines for each of the launched Perf bots.
    d. Add the new baselines to the CL
    e. Upload a second patch set of the CL
    f. Check the CQ bit on the CL

BUG=skia:2225
R=epoger@google.com, halcanary@google.com, bensong@google.com

Author: borenet@google.com

Review URL: https://codereview.chromium.org/297893004

git-svn-id: http://skia.googlecode.com/svn/trunk@14921 2bbb7eff-a529-9590-31e7-b0007b416f81