Avoid unnecessary work in |RenderTextWin::UpdateLayout()| if there are no runs.

ui/gfx/render_text_win.h

 // Copyright (c) 2011 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.
 
 #ifndef UI_GFX_RENDER_TEXT_WIN_H_
 #define UI_GFX_RENDER_TEXT_WIN_H_
 #pragma once
 
 #include <usp10.h>
 
@@ skipping 61 matching lines @@
   virtual SelectionModel LeftEndSelectionModel() OVERRIDE;
   virtual SelectionModel RightEndSelectionModel() OVERRIDE;
   virtual std::vector<Rect> GetSubstringBounds(size_t from, size_t to) OVERRIDE;
   virtual bool IsCursorablePosition(size_t position) OVERRIDE;
   virtual void UpdateLayout() OVERRIDE;
 
  private:
   virtual size_t IndexOfAdjacentGrapheme(size_t index, bool next) OVERRIDE;
 
   void ItemizeLogicalText();
-  void LayoutVisualText(HDC hdc);
+  void LayoutVisualText();
 
   // Return the run index that contains the argument; or the length of the
   // |runs_| vector if argument exceeds the text length or width.
   size_t GetRunContainingPosition(size_t position) const;
   size_t GetRunContainingPoint(const Point& point) const;
 
   // Given a |run|, returns the SelectionModel that contains the logical first
   // or last caret position inside (not at a boundary of) the run.
   // The returned value represents a cursor/caret position without a selection.
   SelectionModel FirstSelectionModelInsideRun(internal::TextRun*);
@@ skipping 25 matching lines @@
 
   scoped_array<int> visual_to_logical_;
   scoped_array<int> logical_to_visual_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderTextWin);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_WIN_H_