MD Settings: Fix canceling of "Add site exception" dialog.

chrome/browser/resources/settings/site_settings/add_site_dialog.js

Index: chrome/browser/resources/settings/site_settings/add_site_dialog.js
diff --git a/chrome/browser/resources/settings/site_settings/add_site_dialog.js b/chrome/browser/resources/settings/site_settings/add_site_dialog.js
index 28ef9c0b9488413724e25871ec773f5b49283266..29e5216c2e76a3a5f849a62d25119a5e7ae40e1d 100644
--- a/chrome/browser/resources/settings/site_settings/add_site_dialog.js
+++ b/chrome/browser/resources/settings/site_settings/add_site_dialog.js
@@ -46,6 +46,11 @@ Polymer({
     }.bind(this));
   },
 
+  /** @private */
+  onCancelTap_: function() {
+    this.$.dialog.cancel();
+  },
+
   /**
    * The tap handler for the Add [Site] button (adds the pattern and closes
    * the dialog).