Behavior property copying fixes

* ensure element has `is` on prototype early as this is sometimes checked in user code.
* ensure properties copied onto elements from info/behaviors are forced to configurable so they can be re-configured by later behaviors.
* add `_noAccessors` optimization for faster property copying

lib/legacy/class.js

@@ -30,7 +30,8 @@ const excludeOnInfo = {
   beforeRegister: true,
   registered: true,
   attributeChanged: true,
-  behaviors: true
+  behaviors: true,
+  _noAccessors: true
 };
 
 const excludeOnBehaviors = Object.assign({
@@ -41,13 +42,19 @@ const excludeOnBehaviors = Object.assign({
 }, excludeOnInfo);
 
 function copyProperties(source, target, excludeProps) {
+  const noAccessors = source._noAccessors;
   for (let p in source) {
-    // NOTE: cannot copy `excludeProps` methods onto prototype at least because
-    // `super.ready` must be called and is not included in the user fn.
     if (!(p in excludeProps)) {
-      let pd = Object.getOwnPropertyDescriptor(source, p);
+      if (noAccessors) {
-      if (pd) {
+        target[p] = source[p];
-        Object.defineProperty(target, p, pd);
+      } else {
+        let pd = Object.getOwnPropertyDescriptor(source, p);
+        if (pd) {
+          // ensure property is configurable so that a later behavior can
+          // re-configure it.
+          pd.configurable = true;
+          Object.defineProperty(target, p, pd);
+        }
       }
     }
   }
@@ -498,6 +505,6 @@ export const Class = function(info, mixin) {
       LegacyElementMixin(HTMLElement);
   klass = GenerateClassFromInfo(info, klass, info.behaviors);
   // decorate klass with registration info
-  klass.is = info.is;
+  klass.is = klass.prototype.is = info.is;
   return klass;
 };

test/unit/behaviors.html

@@ -379,6 +379,20 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       behaviors: [window.BehaviorA]
     });
 
+    Polymer({
+      is: 'no-accessors-behavior',
+      behaviors: [{
+        _noAccessors: true,
+        properties: {
+          nug: String
+        },
+        foo: function() {},
+        bar: true
+      }],
+      _noAccessors: true,
+      zot: 'zot'
+    });
+
 </script>
 
   <test-fixture id="single">
@@ -447,6 +461,12 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     </template>
   </test-fixture>
 
+  <test-fixture id="no-accessors-behavior">
+    <template>
+      <no-accessors-behavior></no-accessors-behavior>
+    </template>
+  </test-fixture>
+
 <script type="module">
 import { Polymer } from '../../polymer-legacy.js';
 
@@ -501,6 +521,15 @@ suite('single behavior element', function() {
     assert.notOk(el.listeners);
   });
 
+  test('properties on objects marked with `_noAccessors` are copied to class', function() {
+    const el = fixture('no-accessors-behavior');
+    assert.ok(el.foo);
+    assert.isTrue(el.bar);
+    assert.equal(el.zot, 'zot');
+    el.setAttribute('nug', 'nug');
+    assert.equal(el.nug, 'nug');
+  });
+
 });
 
 suite('behavior.registered', function() {