Avoid copying certain properties from behaviors

This better matches what Polymer 1.x did for:
* hostAttributes
* listeners
* properties
* observers

lib/legacy/class.js

@@ -10,26 +10,39 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
 import { LegacyElementMixin } from './legacy-element-mixin.js';
 
-const metaProps = {
+const lifecycleProps = {
   attached: true,
   detached: true,
   ready: true,
   created: true,
   beforeRegister: true,
   registered: true,
   attributeChanged: true,
+  listeners: true,
+  hostAttributes: true
 };
 
-const excludeProps = Object.assign({
+const excludeOnInfo = {
+  attached: true,
+  detached: true,
+  ready: true,
+  created: true,
+  beforeRegister: true,
+  registered: true,
+  attributeChanged: true,
   behaviors: true
-}, metaProps);
+};
 
-const lifecycleProps = Object.assign({
+const excludeOnBehaviors = Object.assign({
   listeners: true,
-  hostAttributes: true
-}, metaProps);
+  hostAttributes: true,
+  properties: true,
+  observers: true,
+}, excludeOnInfo);
+
+
 
-function copyProperties(source, target) {
+function copyProperties(source, target, excludeProps) {
   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.
@@ -93,12 +106,12 @@ export function mixinBehaviors(behaviors, klass) {
 // (again same as 1.x)
 function applyBehaviors(proto, behaviors, lifecycle) {
   for (let i=0; i<behaviors.length; i++) {
-    applyInfo(proto, behaviors[i], lifecycle);
+    applyInfo(proto, behaviors[i], lifecycle, excludeOnBehaviors);
   }
 }
 
-function applyInfo(proto, info, lifecycle) {
-  copyProperties(info, proto);
+function applyInfo(proto, info, lifecycle, excludeProps) {
+  copyProperties(info, proto, excludeProps);
   for (let p in lifecycleProps) {
     if (info[p]) {
       lifecycle[p] = lifecycle[p] || [];
@@ -278,7 +291,7 @@ function GenerateClassFromInfo(info, Base, behaviors) {
       if (behaviorList) {
         applyBehaviors(proto, behaviorList, lifecycle);
       }
-      applyInfo(proto, info, lifecycle);
+      applyInfo(proto, info, lifecycle, excludeOnInfo);
       let list = lifecycle.beforeRegister;
       if (list) {
         for (let i=0; i < list.length; i++) {

test/unit/behaviors.html

@@ -65,6 +65,8 @@
         }
       },
 
+      observers: [],
+
       _simpleProperty: 'A',
 
       hostAttributes: {
@@ -372,6 +374,11 @@
       }
     });
 
+    Polymer({
+      is: 'behavior-properties',
+      behaviors: [window.BehaviorA]
+    });
+
 </script>
 
   <test-fixture id="single">
@@ -434,6 +441,12 @@
     </template>
   </test-fixture>
 
+  <test-fixture id="behavior-properties">
+    <template>
+      <behavior-properties></behavior-properties>
+    </template>
+  </test-fixture>
+
 <script type="module">
 import { Polymer } from '../../polymer-legacy.js';
 
@@ -480,6 +493,14 @@
     assert.equal(el.computeA, true);
   });
 
+  test('special properties not copied from behavior to element', function() {
+    const el = fixture('behavior-properties');
+    assert.notOk(el.properties);
+    assert.notOk(el.observers);
+    assert.notOk(el.hostAttributes);
+    assert.notOk(el.listeners);
+  });
+
 });
 
 suite('behavior.registered', function() {