Fixes for cr-settings-page-header

BUG=485381

Review URL: https://codereview.chromium.org/1132613003

Cr-Commit-Position: refs/heads/master@{#329762}

chrome/browser/resources/settings/settings_main/settings_main.html

 <link rel="import" href="chrome://resources/polymer/v0_8/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v0_8/iron-pages/iron-pages.html">
 <link rel="import" href="chrome://md-settings/routes.html">
+<link rel="import" href="chrome://md-settings/settings_page/settings_page_header.html">
 <link rel="import" href="chrome://md-settings/a11y_page/a11y_page.html">
 <link rel="import" href="chrome://md-settings/date_time_page/date_time_page.html">
 <link rel="import" href="chrome://md-settings/downloads_page/downloads_page.html">

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

@@ -70,6 +70,8 @@ Polymer({
    * @private
    */
   getTopPageIcon_: function(pageStack) {
+    if (pageStack.length == 0)
+      return '';
     return pageStack[0].icon;
   },
 
@@ -88,17 +90,21 @@ Polymer({
    * @private
    */
   getCurrentPageTitle_: function(pageStack) {
+    if (pageStack.length == 0)
+      return '';
     return pageStack[0].pageTitle;
   },
 
   /** @private */
   selectedPageChanged_: function() {
-    if (this.selectedPage.subpage) {
+    if (this.selectedPage && this.selectedPage.subpage) {
       // NOTE: Must reassign pageStack rather than doing push() so that the
       // computed property (parentPages) will be notified of the update.
       this.pageStack = this.pageStack.concat(this.selectedPage);
-    } else {
+    } else if (this.selectedPage) {
       this.pageStack = [this.selectedPage];
+    } else {
+      this.pageStack = [];
     }
   },