Prefer static method that hides isTracked detail.

Author: kevinpschaaf

src/lib/collection.html

@@ -96,7 +96,7 @@
       return items;
     },
 
-    applySplices: function(splices) {
+    _applySplices: function(splices) {
       var keySplices = [];
       for (var i=0; i<splices.length; i++) {
         var j, o, key, s = splices[i];
@@ -132,8 +132,11 @@
       || new Polymer.Collection(userArray);
   };
 
-  Polymer.Collection.isTracked = function(userArray) {
-    return Polymer._collections.has(userArray);
+  Polymer.Collection.applySplices = function(userArray, splices) {
+    // Only apply splices & generate keySplices if the array already has a
+    // backing Collection, meaning there is an element monitoring its keys
+    var coll = Polymer._collections.get(userArray);
+    return coll ? coll._applySplices(splices) : null;
   };
 
 </script>

src/lib/experimental/observe-js-behavior.html

@@ -76,8 +76,7 @@
       observer = new ArrayObserver(object);
       observer.open(function(splices) {
         this._notifyObserveJsPath(els, 'splices', {
-          keySplices: Polymer.Collection.isTracked(object) ?
-            Polymer.Collection.get(object).applySplices(splices) : null,
+          keySplices: Polymer.Collection.applySplices(object, splices),
           indexSplices: splices
         });
       }, this);

src/standard/notify-path.html

@@ -332,8 +332,7 @@
           type: 'splice'
         }];
         var change = {
-         keySplices: Polymer.Collection.isTracked(array) ?
-            Polymer.Collection.get(array).applySplices(splices) : null,
+          keySplices: Polymer.Collection.applySplices(array, splices),
           indexSplices: splices
         };
         this.set(path + '.splices', change);