Move |PlatformFont::GetStringWidth()| implementation up into font.cc directly.

ui/gfx/platform_font.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_PLATFORM_FONT_H_
 #define UI_GFX_PLATFORM_FONT_H_
 #pragma once
 
 #include <string>
 
@@ skipping 29 matching lines @@
   // implementations include leading and the Linux one does not.  This may
   // need to be revisited in the future.
   virtual int GetHeight() const = 0;
 
   // Returns the baseline, or ascent, of the font.
   virtual int GetBaseline() const = 0;
 
   // Returns the average character width for the font.
   virtual int GetAverageCharacterWidth() const = 0;
 
-  // Returns the number of horizontal pixels needed to display the specified
-  // string.
-  virtual int GetStringWidth(const string16& text) const = 0;
-
   // Returns the expected number of horizontal pixels needed to display the
   // specified length of characters. Call GetStringWidth() to retrieve the
   // actual number.
   virtual int GetExpectedTextWidth(int length) const = 0;
 
   // Returns the style of the font.
   virtual int GetStyle() const = 0;
 
   // Returns the font name in UTF-8.
   virtual std::string GetFontName() const = 0;
 
   // Returns the font size in pixels.
   virtual int GetFontSize() const = 0;
 
   // Returns the native font handle.
   virtual NativeFont GetNativeFont() const = 0;
 
  protected:
   virtual ~PlatformFont() {}
 
  private:
   friend class base::RefCounted<PlatformFont>;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_PLATFORM_FONT_H_