Reorganize mdv and observe packages

pkg/mdv/lib/src/input_element.dart

+// Copyright (c) 2013, 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.
+
+part of mdv;
+
+/** Extensions to the [InputElement] API. */
+class _InputElementExtension extends _ElementExtension {
+  _InputElementExtension(InputElement node) : super(node);
+
+  InputElement get node => super.node;
+
+  _ValueBinding _valueBinding;
+
+  _CheckedBinding _checkedBinding;
+
+  void bind(String name, model, String path) {
+    switch (name) {
+      case 'value':
+        unbind('value');
+        node.attributes.remove('value');
+        _valueBinding = new _ValueBinding(node, model, path);
+        break;
+      case 'checked':
+        unbind('checked');
+        node.attributes.remove('checked');
+        _checkedBinding = new _CheckedBinding(node, model, path);
+        break;
+      default:
+        super.bind(name, model, path);
+        break;
+    }
+  }
+
+  void unbind(String name) {
+    switch (name) {
+      case 'value':
+        if (_valueBinding != null) {
+          _valueBinding.unbind();
+          _valueBinding = null;
+        }
+        break;
+      case 'checked':
+        if (_checkedBinding != null) {
+          _checkedBinding.unbind();
+          _checkedBinding = null;
+        }
+        break;
+      default:
+        super.unbind(name);
+        break;
+    }
+  }
+
+  void unbindAll() {
+    unbind('value');
+    unbind('checked');
+    super.unbindAll();
+  }
+}