Uses and returns the fractional width in text eliding

ui/gfx/platform_font.h

Index: ui/gfx/platform_font.h
diff --git a/ui/gfx/platform_font.h b/ui/gfx/platform_font.h
index d576bcdf06b3b0e8a4bf8405ab1059eadbeee293..7cee5e06d096b436a7ad7ada42bd34dd78912804 100644
--- a/ui/gfx/platform_font.h
+++ b/ui/gfx/platform_font.h
@@ -52,6 +52,10 @@ class GFX_EXPORT PlatformFont : public base::RefCounted<PlatformFont> {
   // string.
   virtual int GetStringWidth(const base::string16& text) const = 0;
 
+  // Returns the pixel width needed to display the specified string. Note that
+  // the fractional width might be returned in some platforms.
+  virtual float GetStringWidthF(const base::string16& text) const = 0;
+
   // Returns the expected number of horizontal pixels needed to display the
   // specified length of characters. Call GetStringWidth() to retrieve the
   // actual number.