ChromeOS Settings: Fix bluetooth icon updating.

There is a race condition between when Polymer calls observers and when it
updates a two-way bound variable in the parent element.

Bypass the isuse by using the observers parameter instead.

Bug: 896509
Change-Id: I63b13c858b62214d7973af641f67c659de9ea674
Reviewed-on: https://chromium-review.googlesource.com/c/1289410Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600951}

chrome/browser/resources/settings/bluetooth_page/bluetooth_page.js

@@ -162,11 +162,14 @@ Polymer({
   },
 
   /**
+   * @param {boolean} bluetoothToggleState
    * @return {string}
    * @private
    */
-  getIcon_: function() {
-    if (!this.bluetoothToggleState_)
+  getIcon_: function(bluetoothToggleState) {
+    // Don't use |this.bluetoothToggleState_| here, since it has not been
+    // updated yet to the latest value.
+    if (!bluetoothToggleState)
       return 'settings:bluetooth-disabled';
     return 'cr:bluetooth';
   },