Rename rendering/render_*.dart to rendering/*.dart

sky/sdk/lib/framework/rendering/flex.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:sky' as sky;
-import 'render_box.dart';
-import 'render_node.dart';
+import 'box.dart';
+import 'node.dart';
 
 class FlexBoxParentData extends BoxParentData with ContainerParentDataMixin<RenderBox> {
   int flex;
   void merge(FlexBoxParentData other) {
     if (other.flex != null)
       flex = other.flex;
     super.merge(other);
   }
 }
 
@@ skipping 93 matching lines @@
   }
 
   void hitTestChildren(HitTestResult result, { sky.Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
   void paint(RenderNodeDisplayList canvas) {
     defaultPaint(canvas);
   }
 }