rebaseline_server: return rebaseline results faster, and reload UI page automatically...

rebaseline_server: return rebaseline results faster, and reload UI page automatically after

Old way:
Wait until server has loaded the updated results before telling the user the rebaseline
was successful, and trust the user to reload the page before submitting more baselines.

New way:
Make server load the updated results in a separate thread, and automatically reload the page
so that the user can submit more baselines if she wants to.

(SkipBuildbotRuns)
NOTRY=True
NOTREECHECKS=True
R=bsalomon@google.com

Author: epoger@google.com

Review URL: https://codereview.chromium.org/117453002

git-svn-id: http://skia.googlecode.com/svn/trunk@12717 2bbb7eff-a529-9590-31e7-b0007b416f81