Uses and returns the fractional width in text eliding

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 a97da2eedcf1ad9e2ecafb5e748a1bb33675b3a6..e9fee49904c633c7f7cd2c5a5bfdb00f68776ada 100644
--- a/ui/gfx/platform_font_win.cc
+++ b/ui/gfx/platform_font_win.cc
@@ -19,6 +19,7 @@
 #include "base/win/win_util.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/font.h"
+#include "ui/gfx/font_list.h"
 #include "ui/gfx/win/scoped_set_map_mode.h"
 
 namespace {
@@ -154,6 +155,11 @@ int PlatformFontWin::GetStringWidth(const base::string16& text) const {
                                 Font(const_cast<PlatformFontWin*>(this)));
 }
 
+float PlatformFontWin::GetStringWidthF(const base::string16& text) const {
+  return Canvas::GetStringWidthF(
+      text, FontList(Font(const_cast<PlatformFontWin*>(this))));
+}
+
 int PlatformFontWin::GetExpectedTextWidth(int length) const {
   return length * std::min(font_ref_->GetDluBaseX(),
                            GetAverageCharacterWidth());