GitLab

We have a histogram reporting 'entry age on Open of an existing entry' by
looking at individual files on the filesystem. Change to report once for each
entry.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/23717040

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222166 0039d316-1c4b-4281-b951-d872f2087c98