Add comment. Ensure Date deserializes to String for correctness.

src/micro/attributes.html

@@ -243,7 +243,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
         case 'object':
           if (value instanceof Date) {
-            return value;
+            return value.toString();
           } else if (value) {
             try {
               return JSON.stringify(value);

src/standard/configure.html

@@ -153,6 +153,9 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
                   var value = (p === x.effect.value) ? config[p] :
                     this._get(x.effect.value, config);
                   if (x.effect.kind == 'attribute') {
+                    // For attribute bindings, flow through the same ser/deser
+                    // process to ensure the value is the same as if it were
+                    // bound through the attribute
                     value = node.deserialize(node.serialize(value),
                       node._propertyInfo[name].type);
                   }