[MD settings] refine routing function

chrome/browser/resources/settings/settings_page/settings_animated_pages.js

Index: chrome/browser/resources/settings/settings_page/settings_animated_pages.js
diff --git a/chrome/browser/resources/settings/settings_page/settings_animated_pages.js b/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
index 27869cd148599361af67adf5b853bb64e28549be..89b3f35e29af908ccc684bb29590a56ec708c5a4 100644
--- a/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
+++ b/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
@@ -146,8 +146,15 @@ Polymer({
    * Buttons in this pageset should use this method to transition to subpages.
    */
   setSubpageChain: function(subpage) {
+    var node = event.currentTarget;

[dpapad, 2016/05/27 00:44:22]

Where is |event| coming from?

[dschuyler, 2016/05/27 01:30:49]

I commented that it's a global, but there
is still the question of whether this should
be plumbed through from the caller instead
of using the global. (Note that we're not
creating the global for this, it already 
exists).

Done.

+    var page;
+    while (node) {
+      if (node.dataset && node.dataset.page)
+        page = node.dataset.page;
+      node = node.host || node.parentNode;

[dpapad, 2016/05/27 00:44:22]

What is the expected type(s) of |node|? I recognize "parentNode" as
https://developer.mozilla.org/en-US/docs/Web/API/Node/parentNode, but don't
recognize "host". Could you add @type annotatino or a comment?

[dschuyler, 2016/05/27 01:30:49]

Done.

+    }
     this.currentRoute = {
-      page: this.currentRoute.page,
+      page: page,
       section: subpage.length > 0 ? this.section : '',
       subpage: subpage,
     };