Make classList a getter so it can be lazy; dom mutation api's only cause distribution on parent.

src/lib/dom-api.html

@@ -29,7 +29,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       if (this.patch) {
         this.patch();
       }
-      this.classList = new DomApi.ClassList(this);
     };
 
     DomApi.prototype = {
@@ -369,8 +368,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         }
       },
 
-      // TODO(sorvell): make Polymer utils use these...
-
       setAttribute: function(name, value) {
         this.node.setAttribute(name, value);
         this._distributeParent();
@@ -383,12 +380,22 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
       _distributeParent: function() {
         if (this.parentNode && this.parentNode.shadyRoot) {
-          this.parentNode.distributeContent();
+          this._lazyDistribute(this.parentNode);
         }
       }
 
     };
 
+    Object.defineProperty(DomApi.prototype, 'classList', {
+      get: function() {
+        if (!this._classList) {
+          this._classList = new DomApi.ClassList(this);
+        }
+        return this._classList;
+      },
+      configurable: true
+    });
+
     DomApi.ClassList = function(host) {
       this.domApi = host;
       this.node = host.node;