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

ui/gfx/render_text_win.h

Index: ui/gfx/render_text_win.h
===================================================================
--- ui/gfx/render_text_win.h	(revision 145906)
+++ ui/gfx/render_text_win.h	(working copy)
@@ -98,8 +98,8 @@
   // 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;