Capture failed webpages with their stacktraces in a JSON file
Capture failed webpages with their stacktraces in a JSON file

* Capture failed webpages and their stacktraces in a JSON file. 
* Do not check if .boto file is valid if do_not_upload_to_gs flag is True. 

(SkipBuildbotRuns)

R=borenet@google.com

Review URL: https://codereview.chromium.org/14847007

git-svn-id: 32fc27f4dcfb6c0385cd9719852b95fe6680452d@8962 2bbb7eff-a529-9590-31e7-b0007b416f81

google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot