Switch prefs.js to Object.observe now that observe-js is no longer a dep.

chrome/browser/resources/settings/prefs/prefs.js

Index: chrome/browser/resources/settings/prefs/prefs.js
diff --git a/chrome/browser/resources/settings/prefs/prefs.js b/chrome/browser/resources/settings/prefs/prefs.js
index febc22d41b1e70e46394148759d257e9ffb05762..849f4536aaa13f7a3c6036553ee29c8bca9791d5 100644
--- a/chrome/browser/resources/settings/prefs/prefs.js
+++ b/chrome/browser/resources/settings/prefs/prefs.js
@@ -97,40 +97,32 @@
         }
 
         if (shouldObserve) {
-          let keyObserver = new ObjectObserver(root);
-          keyObserver.open(
-              this.propertyChangeCallback_.bind(this, prefObj.key));
+          Object.observe(root, this.propertyChangeCallback_, ['update']);
         }
       }, this);
     },
 
     /**
      * Called when a property of a pref changes.
-     * @param {string} propertyPath The path before the property names.
-     * @param {!Array<string>} added An array of keys which were added.
-     * @param {!Array<string>} removed An array of keys which were removed.
-     * @param {!Array<string>} changed An array of keys of properties whose
-     *     values changed.
-     * @param {function(string) : *} getOldValueFn A function which takes a
-     *     property name and returns the old value for that property.
+     * @param {!Array<!Object>} changes An array of objects describing changes.
+     *     @see http://www.html5rocks.com/en/tutorials/es7/observe/
      * @private
      */
-    propertyChangeCallback_: function(
-        propertyPath, added, removed, changed, getOldValueFn) {
-      for (let property in changed) {
+    propertyChangeCallback_: function(changes) {
+      changes.forEach(function(change) {
         // UI should only be able to change the value of a setting for now, not
         // disabled, etc.
-        assert(property == 'value');
+        assert(change.name == 'value');
 
-        let newValue = changed[property];
+        let newValue = change.object[change.name];
         assert(newValue !== undefined);
 
         chrome.settingsPrivate.setPref(
-            propertyPath,
+            change.object['key'],
             newValue,
             /* pageId */ '',
             /* callback */ function() {});
-      }
+      });
     },
   });
 })();