Changed interfaces to abstract classes where possible in {lib,samples,pkg}

samples/ui_lib/touch/TouchUtil.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Wraps a callback with translations of mouse events to touch events. Use
  * this function to invoke your callback that expects touch events after
  * touch events are created from the actual mouse events.
  */
 EventListener mouseToTouchCallback(EventListener callback) {
@@ skipping 86 matching lines @@
   while (target != null) {
     if (target == node) {
       return true;
     }
     target = target.parent;
   }
 
   return false;
 }
 
-interface Touchable {
+abstract class Touchable {
   /**
    * Provide the HTML element that should respond to touch events.
    */
   Element getElement();
 
   /**
    * The object has received a touchend event.
    */
   void onTouchEnd();
 
   /**
    * The object has received a touchstart event.
    * Returns return true if you want to allow a drag sequence to begin,
    *      false you want to disable dragging for the duration of this touch.
    */
   bool onTouchStart(TouchEvent e);
 }
 
-interface Draggable extends Touchable {
+abstract class Draggable implements Touchable {
   /**
    * The object's drag sequence is now complete.
    */
   void onDragEnd();
 
   /**
    * The object has been dragged to a new position.
    */
   void onDragMove();
 
@@ skipping 96 matching lines @@
   int get which => wrapped.which;
 
   bool get altKey => wrapped.altKey;
 
   bool get ctrlKey => wrapped.ctrlKey;
 
   bool get metaKey => wrapped.metaKey;
 
   bool get shiftKey => wrapped.shiftKey;
 }