Fix a few strong mode errors in dart:html

tools/dom/templates/html/impl/impl_DeviceOrientationEvent.darttemplate

 // 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.
 
 // WARNING: Do not edit - generated code.
 
 part of $LIBRARYNAME;
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
   factory $CLASSNAME(String type,
       {bool canBubble: true, bool cancelable: true, num alpha: 0, num beta: 0,
       num gamma: 0, bool absolute: false}) {
-    var e = document._createEvent("DeviceOrientationEvent");
+    DeviceOrientationEvent e = document._createEvent("DeviceOrientationEvent");
     e._initDeviceOrientationEvent(type, canBubble, cancelable, alpha, beta,
         gamma, absolute);
     return e;
   }
 $!MEMBERS
 }