Fix treemaps view of the flakiness dashboard.

This broke when times_ms.json files were changes to store and
require a build number when uploading/querying. Unfortunately,
they store 0 instead of the actual build number and buildnumber=latest
appears to not work, so use buildnumber=0 for now.

NOTRY=true

Review URL: https://codereview.chromium.org/431023002

git-svn-id: svn://svn.chromium.org/blink/trunk@179338 bbb929c8-8fbe-4397-9dbb-9b2b20218538