RenderTextMac: Fix crash when passed an invalid font.

ui/gfx/render_text.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_H_
 #define UI_GFX_RENDER_TEXT_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 227 matching lines @@
   const base::string16& text() const { return text_; }
   void SetText(const base::string16& text);
   void AppendText(const base::string16& text);
 
   HorizontalAlignment horizontal_alignment() const {
     return horizontal_alignment_;
   }
   void SetHorizontalAlignment(HorizontalAlignment alignment);
 
   const FontList& font_list() const { return font_list_; }
-  void SetFontList(const FontList& font_list);
+  virtual void SetFontList(const FontList& font_list);
 
   bool cursor_enabled() const { return cursor_enabled_; }
   void SetCursorEnabled(bool cursor_enabled);
 
   SkColor selection_color() const { return selection_color_; }
   void set_selection_color(SkColor color) { selection_color_ = color; }
 
   SkColor selection_background_focused_color() const {
     return selection_background_focused_color_;
   }
@@ skipping 601 matching lines @@
   // Lines computed by EnsureLayout. These should be invalidated upon
   // OnLayoutTextAttributeChanged and OnDisplayTextAttributeChanged calls.
   std::vector<internal::Line> lines_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderText);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_H_