Fix QuicConnectionHelper's alarm implementation
to properly allow alarms to be re-secheduled for an earlier time.

Review URL: https://codereview.chromium.org/26331009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228641 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228641