Fix Pango font rendering with HiDPi displays on Linux.

ui/gfx/linux_font_delegate.h

 // Copyright 2013 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_LINUX_FONT_DELEGATE_H_
 #define UI_GFX_LINUX_FONT_DELEGATE_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 10 matching lines @@
   // Sets the dynamically loaded singleton that provides font preferences.
   // This pointer is not owned, and if this method is called a second time,
   // the first instance is not deleted.
   static void SetInstance(LinuxFontDelegate* instance);
 
   // Returns a LinuxFontDelegate instance for the toolkit used in
   // the user's desktop environment.
   //
   // Can return NULL, in case no toolkit has been set. (For example, if we're
   // running with the "--ash" flag.)
-  static const LinuxFontDelegate* instance();
+  static LinuxFontDelegate* instance();
 
   // Returns the default font rendering settings.
   virtual FontRenderParams GetDefaultFontRenderParams() const = 0;
 
   // Returns details about the default UI font. |style_out| holds a bitfield of
   // gfx::Font::Style values.
   virtual void GetDefaultFontDescription(
       std::string* family_out,
       int* size_pixels_out,
       int* style_out,
-      FontRenderParams* params_out) const = 0;
+      FontRenderParams* params_out) = 0;
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_LINUX_FONT_DELEGATE_H_