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

sky/sdk/lib/framework/rendering/paragraph.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 RenderInline extends RenderNode {
   String data;
 
   RenderInline(this.data);
 }
 
 class RenderParagraph extends RenderBox {
 
   RenderParagraph({
@@ skipping 37 matching lines @@
     size = constraints.constrain(new sky.Size(_layoutRoot.rootElement.width, _layoutRoot.rootElement.height));
   }
 
   void paint(RenderNodeDisplayList canvas) {
     // _layoutRoot.rootElement.style['color'] = 'rgba(' + ...color... + ')';
     _layoutRoot.paint(canvas);
   }
 
   // we should probably expose a way to do precise (inter-glpyh) hit testing
 }