Moved most of html lib generating scripts into tools.

tools/dom/templates/html/impl/impl_EventTarget.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.
 
 part of html;
 
 /**
  * Base class that supports listening for and dispatching browser events.
  *
  * Events can either be accessed by string name (using the indexed getter) or by
@@ skipping 62 matching lines @@
  * [$dom_addEventListener], [$dom_dispatchEvent], and
  * [$dom_removeEventListener]) for compile-time type checks and a more concise
  * API.
  */ 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   /** @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent */
   Events get on => new Events(this);
 $!MEMBERS
 }