RenderTextWin: Use a font that can at least partially display the run, if possible.

ui/gfx/render_text_win.h

 // Copyright (c) 2012 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 80 matching lines @@
   virtual void EnsureLayout() OVERRIDE;
   virtual void DrawVisualText(Canvas* canvas) OVERRIDE;
 
  private:
   void ItemizeLogicalText();
   void LayoutVisualText();
 
   // Helper function to update the font on a text run after font substitution.
   void ApplySubstituteFont(internal::TextRun* run, const Font& font);
 
-  // Returns whether |run| contains missing glyphs.
-  bool HasMissingGlyphs(internal::TextRun* run) const;
+  // Returns the number of characters in |run| that have missing glyphs.
+  int CountCharsWithMissingGlyphs(internal::TextRun* run) const;
 
   // Returns a vector of linked fonts corresponding to |font|.
   const std::vector<Font>* GetLinkedFonts(const Font& font) const;
 
   // 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 GetRunContainingCaret(const SelectionModel& caret) const;
   size_t GetRunContainingPoint(const Point& point) const;
 
   // Given a |run|, returns the SelectionModel that contains the logical first
@@ skipping 28 matching lines @@
   scoped_array<int> logical_to_visual_;
 
   bool needs_layout_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderTextWin);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_WIN_H_