cherry pick to fix memory leak

pkg/web_components/lib/platform.concat.js

 /**
  * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
  * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
  * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
  * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
  * Code distributed by Google as part of the polymer project is also
  * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
  */
 
 window.Platform = window.Platform || {};
@@ skipping 2309 matching lines @@
   'use strict';
 
   var setEndOfMicrotask = scope.setEndOfMicrotask
   var wrapIfNeeded = scope.wrapIfNeeded
   var wrappers = scope.wrappers;
 
   var registrationsTable = new WeakMap();
   var globalMutationObservers = [];
   var isScheduled = false;
 
-  function scheduleCallback(observer) {
+  function scheduleCallback() {
     if (isScheduled)
       return;
     setEndOfMicrotask(notifyObservers);
     isScheduled = true;
   }
 
   // http://dom.spec.whatwg.org/#mutation-observers
   function notifyObservers() {
     isScheduled = false;
 
-    do {
-      var notifyList = globalMutationObservers.slice();
-      var anyNonEmpty = false;
+    while (globalMutationObservers.length) {
+      var notifyList = globalMutationObservers;
+      globalMutationObservers = [];
+
+      // Deliver changes in birth order of the MutationObservers.
+      notifyList.sort(function(x, y) { return x.uid_ - y.uid_; });
+
       for (var i = 0; i < notifyList.length; i++) {
         var mo = notifyList[i];
         var queue = mo.takeRecords();
         removeTransientObserversFor(mo);
         if (queue.length) {
           mo.callback_(queue, mo);
-          anyNonEmpty = true;
         }
       }
-    } while (anyNonEmpty);
+    }
   }
 
+
   /**
    * @param {string} type
    * @param {Node} target
    * @constructor
    */
   function MutationRecord(type, target) {
     this.type = type;
     this.target = target;
     this.addedNodes = new wrappers.NodeList();
     this.removedNodes = new wrappers.NodeList();
@@ skipping 85 matching lines @@
         // true, or type is "characterData" and options's characterDataOldValue
         // is true, set the paired string of registered observer's observer in
         // interested observers to oldValue.
         if (type === 'attributes' && options.attributeOldValue ||
             type === 'characterData' && options.characterDataOldValue) {
           associatedStrings[observer.uid_] = data.oldValue;
         }
       }
     }
 
-    var anyRecordsEnqueued = false;
+    var anyObserversEnqueued = false;
 
     // 4.
     for (var uid in interestedObservers) {
       var observer = interestedObservers[uid];
       var record = new MutationRecord(type, target);
 
       // 2.
       if ('name' in data && 'namespace' in data) {
         record.attributeName = data.name;
         record.attributeNamespace = data.namespace;
@@ skipping 13 matching lines @@
 
       // 6.
       if (data.nextSibling)
         record.nextSibling = data.nextSibling;
 
       // 7.
       if (associatedStrings[uid] !== undefined)
         record.oldValue = associatedStrings[uid];
 
       // 8.
+      if (!observer.records_.length) {
+        globalMutationObservers.push(observer);
+        anyObserversEnqueued = true;
+      }
       observer.records_.push(record);
-
-      anyRecordsEnqueued = true;
     }
 
-    if (anyRecordsEnqueued)
+    if (anyObserversEnqueued)
       scheduleCallback();
   }
 
   var slice = Array.prototype.slice;
 
   /**
    * @param {!Object} options
    * @constructor
    */
   function MutationObserverOptions(options) {
@@ skipping 43 matching lines @@
   /**
    * The class that maps to the DOM MutationObserver interface.
    * @param {Function} callback.
    * @constructor
    */
   function MutationObserver(callback) {
     this.callback_ = callback;
     this.nodes_ = [];
     this.records_ = [];
     this.uid_ = ++uidCounter;
-
-    // This will leak. There is no way to implement this without WeakRefs :'(
-    globalMutationObservers.push(this);
   }
 
   MutationObserver.prototype = {
     constructor: MutationObserver,
 
     // http://dom.spec.whatwg.org/#dom-mutationobserver-observe
     observe: function(target, options) {
       target = wrapIfNeeded(target);
 
       var newOptions = new MutationObserverOptions(options);
@@ skipping 9677 matching lines @@
   // exports
 
   scope.marshal = marshal;
   // `module` confuses commonjs detectors
   scope.modularize = module;
   scope.using = using;
 
 })(window);
 
 //# sourceMappingURL=platform.concat.js.map