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

ui/gfx/platform_font_win.cc

Index: ui/gfx/platform_font_win.cc
diff --git a/ui/gfx/platform_font_win.cc b/ui/gfx/platform_font_win.cc
index f2b809b84b93952d6e662cb368d59142b6c18f00..0648a8bf14c43f3967c8a42ab281069641ddf25e 100644
--- a/ui/gfx/platform_font_win.cc
+++ b/ui/gfx/platform_font_win.cc
@@ -509,11 +509,12 @@ PlatformFontWin::HFontRef* PlatformFontWin::CreateHFontRefFromSkia(
 
   // The metrics retrieved from skia don't have the average character width. In
   // any case if we get the average character width from skia then use that or
-  // use the text extent technique as documented by microsoft. See
-  // GetAverageCharWidthInDialogUnits for details.
+  // the average character width in the TEXTMETRIC structure.
+  // TODO(ananta)

[Alexei Svitkine (slow), 2015/01/29 20:52:10]

Nit:

Usually, there's a : after the TODO(name) and the text follows on the same line.

[ananta, 2015/01/29 21:04:58]

Done.

+  // Investigate whether it is possible to retrieve this value from
+  // DirectWrite.
   const int ave_char_width =
-      skia_metrics.fAvgCharWidth == 0 ?
-          HFontRef::GetAverageCharWidthInDialogUnits(gdi_font)
+      skia_metrics.fAvgCharWidth == 0 ? font_metrics.tmAveCharWidth
               : skia_metrics.fAvgCharWidth;
 
   int style = 0;