For DirectWrite font metrics use the average character width from the TEXTMETRIC structure.

ui/gfx/platform_font_win_unittest.cc

 // 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.
 
 #include "ui/gfx/platform_font_win.h"
 
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
@@ skipping 132 matching lines @@
 
     scoped_refptr<PlatformFontWin::HFontRef> h_font_gdi(
         PlatformFontWin::CreateHFontRefFromGDI(font, font_metrics));
 
     scoped_refptr<PlatformFontWin::HFontRef> h_font_skia(
         PlatformFontWin::CreateHFontRefFromSkia(font, font_metrics));
 
     EXPECT_EQ(h_font_gdi->font_size(), h_font_skia->font_size());
     EXPECT_EQ(h_font_gdi->style(), h_font_skia->style());
     EXPECT_EQ(h_font_gdi->font_name(), h_font_skia->font_name());
+    EXPECT_EQ(h_font_gdi->ave_char_width(), h_font_skia->ave_char_width());
 
     EXPECT_LE(abs(h_font_gdi->cap_height() - h_font_skia->cap_height()), 1);
     EXPECT_LE(abs(h_font_gdi->baseline() - h_font_skia->baseline()), 1);
     EXPECT_LE(abs(h_font_gdi->height() - h_font_skia->height()), 1);
   }
 }
 
 }  // namespace gfx