Removed IllegalAccessException and UnsupportedOperationException.

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 {
 $!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 const UnsupportedOperationException(
+        throw new UnsupportedError(
             'offsetX is only supported on elements');
       }
       return this.clientX - this.target.getBoundingClientRect().left;
     }
   }
 
   int get offsetY {
     if (JS('bool', '!!#.offsetY', this)) {
       return JS('int', '#.offsetY', this);
     } else {
       // Firefox does not support offsetY.
       var target = this.target;
       if (!(target is Element)) {
-        throw const UnsupportedOperationException(
+        throw new UnsupportedError(
             'offsetY is only supported on elements');
       }
       return this.clientY - this.target.getBoundingClientRect().top;
     }
   }
 }