Added custom tags helper classes to the Observatory

runtime/observatory/lib/src/elements/shims/binding.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:core';
+import 'dart:html';
+import 'dart:js';
+import 'dart:mirrors';
+import 'package:js/js.dart';
+import 'package:js_util/js_util.dart';
+import 'package:polymer/polymer.dart';
+
+class Binding {
+  final String attribute;
+  final String property;
+  const Binding (attribute, [String property])
+      : attribute = attribute,
+        property = property == null ? attribute : property;
+}
+
+///This is a temporary bridge between Polymer Bindings and the wrapper entities.
+class Binder<T extends HtmlElement> {
+  final List<Binding> attributes;
+  final callback;
+
+  Binder(List<Binding> attributes)
+      : attributes = attributes,
+        callback = _createCallback(T, attributes);
+
+  registerCallback(T element) {
+    assert(element != null);
+    setValue(element, 'bind', callback);
+  }
+
+  static _createCallback(Type T, List<Binding> attributes){
+    final target = reflectClass(T);
+    final setters = <String, Symbol>{};
+    for (Binding binding in attributes){
+      var member = target.instanceMembers[new Symbol(binding.property + '=')];
+      if (!member.isSetter)
+        throw new ArgumentError(
+          '${binding.property} is not a Setter for class $T');
+      setters[binding.attribute] = new Symbol(binding.property);
+    }
+    return allowInteropCaptureThis((_this, name, value, [other]) {
+      final setter = setters[name];
+      if (setter == null) return;
+      Bindable bindable;
+      if (identical(1, 1.0)) { // dart2js
+        bindable = getValue(getValue(value, '__dartBindable'), 'o') as Bindable;
+      } else { // vm
+        bindable = getValue(value, '__dartBindable');
+      }
+      var obj = reflect(_this);
+      obj.setField(setter, bindable.value);
+      bindable.open((value) {
+        obj.setField(setter, value);
+      });
+    });
+  }
+}