Build correct URL for cacheinvalidation endpoint.

Build URL for sending client-to-server cacheinvalidation messages.

BUG=325020
R=rlarocque@chromium.org

Review URL: https://codereview.chromium.org/182333003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255825 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255825