Currently the histograms are binned together for all errors, but
knowing open-specific errors is helpful for dealing with problems on
open.
BUG=159490
Review URL: https://chromiumcodereview.appspot.com/11468024
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171862 0039d316-1c4b-4281-b951-d872f2087c98