Cpu metric: Change assert total_time > 0 to conditional

BUG=304342

Review URL: https://codereview.chromium.org/26093002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228378 0039d316-1c4b-4281-b951-d872f2087c98
Blink roll 159484:159522

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=159485:159522&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/26438003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228379 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228380 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228379
SVN changes up to revision 228380