Added minimal documentation to the KeyboardEvent class.

tools/dom/templates/html/dart2js/impl_KeyboardEvent.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.
 
 
+/**
+ * An event that describes user interaction with the keyboard.
+ *
+ * The [type] of the event identifies what kind of interaction occurred.
+ *
+ * See also:
+ *
+ * * [KeyboardEvent](https://developer.mozilla.org/en/DOM/KeyboardEvent) at MDN.
+ */
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   factory $CLASSNAME(String type,
       {Window view, bool canBubble: true, bool cancelable: true,
       String keyIdentifier: "", int keyLocation: 1, bool ctrlKey: false,
       bool altKey: false, bool shiftKey: false, bool metaKey: false,
       bool altGraphKey: false}) {
     if (view == null) {
       view = window;
     }
@@ skipping 23 matching lines @@
     }
   }
 
   @DomName('KeyboardEvent.keyCode')
   int get keyCode => $dom_keyCode;
 
   @DomName('KeyboardEvent.charCode')
   int get charCode => $dom_charCode;
 $!MEMBERS
 }