Mac: Fix PlatformFontMac::DeriveFont.

ui/gfx/platform_font_mac.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_PLATFORM_FONT_MAC_H_
 #define UI_GFX_PLATFORM_FONT_MAC_H_
 
 #include "base/compiler_specific.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/macros.h"
@@ skipping 23 matching lines @@
   std::string GetActualFontNameForTesting() const override;
   int GetFontSize() const override;
   const FontRenderParams& GetFontRenderParams() override;
   NativeFont GetNativeFont() const override;
 
  private:
   PlatformFontMac(const std::string& font_name,
                   int font_size,
                   int font_style,
                   Font::Weight font_weight);
+
+  PlatformFontMac(NativeFont font,
+                  const std::string& font_name,
+                  int font_size,
+                  int font_style,
+                  Font::Weight font_weight);
+
   ~PlatformFontMac() override;
 
   // Calculates and caches the font metrics and inits |render_params_|.
   void CalculateMetricsAndInitRenderParams();
 
   // The NSFont instance for this object. If this object was constructed from an
   // NSFont instance, this holds that NSFont instance. Otherwise this NSFont
   // instance is constructed from the name, size, and style, and if there is no
   // active font that matched those criteria, this object may be nil.
   base::scoped_nsobject<NSFont> native_font_;
 
   // The name/size/style trio that specify the font. Initialized in the
   // constructors.
-  std::string font_name_;  // Corresponds to -[NSFont fontFamily].
-  int font_size_;
-  int font_style_;
-  Font::Weight font_weight_;
+  const std::string font_name_;  // Corresponds to -[NSFont fontFamily].
+  const int font_size_;
+  const int font_style_;
+  const Font::Weight font_weight_;
 
   // Cached metrics, generated in CalculateMetrics().
   int height_;
   int ascent_;
   int cap_height_;
   int average_width_;
 
   // Details about how the font should be rendered.
   FontRenderParams render_params_;
 
   DISALLOW_COPY_AND_ASSIGN(PlatformFontMac);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_PLATFORM_FONT_MAC_H_