Fix host installation prompt cancelation in CRD webapp.

When host installation is cancelled HostSetupDialog dialog is supposed
to hide the installation prompt, but previously it only updated
internal state, but not webapp UI state.

BUG=350211
R=jamiewalch@chromium.org

Review URL: https://codereview.chromium.org/196313002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256372 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256372