Uses and returns the fractional width in text eliding

ui/gfx/render_text.h

Index: ui/gfx/render_text.h
diff --git a/ui/gfx/render_text.h b/ui/gfx/render_text.h
index df23ff3ef88b431135716432a117ea9b4a07b835..b2ff070be3767f860fd6768dc14d5bcbbafc7179 100644
--- a/ui/gfx/render_text.h
+++ b/ui/gfx/render_text.h
@@ -25,6 +25,7 @@
 #include "ui/gfx/rect.h"
 #include "ui/gfx/selection_model.h"
 #include "ui/gfx/shadow_value.h"
+#include "ui/gfx/size_f.h"
 #include "ui/gfx/text_constants.h"
 #include "ui/gfx/vector2d.h"
 
@@ -326,6 +327,12 @@ class GFX_EXPORT RenderText {
   // shadows.
   virtual Size GetStringSize() = 0;
 
+  // This is same as GetStringSize except that floating-point size is returned.
+  // The default implementation is same as GetStringSize. Certain platforms that
+  // compute the text size as floating-point values, like Mac, will override
+  // this method.
+  virtual SizeF GetStringSizeF();
+
   // Returns the width of the content (which is the wrapped width in multiline
   // mode). Reserves room for the cursor if |cursor_enabled_| is true.
   int GetContentWidth();