Fix test failures by feature detecting instance properties accessors.

Can't rely on `__proto__` on IE10, but that browser doesn't need to avoid `properties`.

src/standard/configure.html

@@ -43,6 +43,11 @@
 
   var usePolyfillProto = Polymer.Settings.usePolyfillProto;
 
+  // When true, `this.properties` is bad juju due to obsolete `properties`
+  // accessors on instances of HTMLElement
+  var avoidInstanceProperties =
+    Boolean(Object.getOwnPropertyDescriptor(document.body, 'properties'));
+
   Polymer.Base._addFeature({
 
     // storage for configuration
@@ -106,7 +111,8 @@
       // property, and b.) the `properties` accessor is on instances rather
       // than `HTMLElement.prototype`; going under the instance to the prototype
       // avoids the problem.
-      this._configureProperties(this.__proto__.properties, config);
+      this._configureProperties(avoidInstanceProperties ?
+        this.__proto__.properties : this.properties, config);
       // TODO(sorvell): it *may* be faster to loop over _propertyInfo but
       // there are some test issues.
       //this._configureProperties(this._propertyInfo, config);