rebaseline_server: improve thread locks to allow read access during updates
(SkipBuildbotRuns)
TBR=jcgregorio

Review URL: https://codereview.chromium.org/66803004

git-svn-id: http://skia.googlecode.com/svn/trunk@12195 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed