WebUI cr-dialog: Cancel dialog on any 'popstate' event.

ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js

Index: ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
diff --git a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
index 5deb50cdea1c893c1fb7a77c852029fbd5397bd3..fc13095d5eec9c815c1c54e713b4f6206a0a0f11 100644
--- a/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
+++ b/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.js
@@ -15,6 +15,16 @@ Polymer({
   is: 'cr-dialog',
   extends: 'dialog',
 
+  /** @override */
+  created: function() {
+    // If the active history entry changes (i.e. user clicks back button),
+    // all open dialogs should be cancelled.
+    window.addEventListener('popstate', function() {

[Dan Beam, 2016/08/16 01:30:43]

tsergeant@/calamity@/mahmadi@: does this behavior work for your UI?

if not (and we only want to do this in settings), tommycli@ could probably:

1) make this an option (i.e. <dialog is="cr-dialog" no-close-on-popstate>)
2) make a settings specific version of <cr-dialog> through inheritance or
composition

the important thing to note is that this will close every dialog when a
'popstate' event (generally: pressing back while using
history.{push,replace}State())

https://developer.mozilla.org/en-US/docs/Web/Events/popstate

+      if (this.open)
+        this.cancel();
+    }.bind(this));
+  },
+
   cancel: function() {
     this.fire('cancel');
     HTMLDialogElement.prototype.close.call(this, '');