Uses and returns the fractional width in text eliding

ui/gfx/platform_font_pango.cc

Index: ui/gfx/platform_font_pango.cc
diff --git a/ui/gfx/platform_font_pango.cc b/ui/gfx/platform_font_pango.cc
index 856acc2c432a209b0e451bfa86c8883db92d7e90..d8764b3c8a43239ec423846423148cac447285a2 100644
--- a/ui/gfx/platform_font_pango.cc
+++ b/ui/gfx/platform_font_pango.cc
@@ -18,6 +18,7 @@
 #include "third_party/skia/include/core/SkTypeface.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/font.h"
+#include "ui/gfx/font_list.h"
 #include "ui/gfx/pango_util.h"
 
 #if defined(TOOLKIT_GTK)
@@ -202,6 +203,11 @@ int PlatformFontPango::GetStringWidth(const base::string16& text) const {
                                 Font(const_cast<PlatformFontPango*>(this)));
 }
 
+float PlatformFontPango::GetStringWidthF(const base::string16& text) const {
+  return Canvas::GetStringWidthF(
+      text, FontList(Font(const_cast<PlatformFontPango*>(this))));
+}
+
 int PlatformFontPango::GetExpectedTextWidth(int length) const {
   double char_width = const_cast<PlatformFontPango*>(this)->GetAverageWidth();
   return round(static_cast<float>(length) * char_width);