Merging dart:html interfaces and implementations

sdk/lib/html/templates/html/dart2js/impl_MouseEvent.darttemplate

 // Copyright (c) 2012, 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.
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+  factory $CLASSNAME(String type, Window view, int detail, int screenX,
+      int screenY, int clientX, int clientY, int button, [bool canBubble = true,
+      bool cancelable = true, bool ctrlKey = false, bool altKey = false,
+      bool shiftKey = false, bool metaKey = false,
+      EventTarget relatedTarget = null]) =>
+      _$(CLASSNAME)FactoryProvider.create$CLASSNAME(
+          type, view, detail, screenX, screenY,
+          clientX, clientY, button, canBubble, cancelable,
+          ctrlKey, altKey, shiftKey, metaKey,
+          relatedTarget);
 $!MEMBERS
 
   int get offsetX {
   if (JS('bool', '!!#.offsetX', this)) {
       return JS('int', '#.offsetX', this);
     } else {
       // Firefox does not support offsetX.
       var target = this.target;
       if (!(target is Element)) {
         throw new UnsupportedError(
@@ skipping 10 matching lines @@
       // Firefox does not support offsetY.
       var target = this.target;
       if (!(target is Element)) {
         throw new UnsupportedError(
             'offsetY is only supported on elements');
       }
       return this.clientY - this.target.getBoundingClientRect().top;
     }
   }
 }