Uses and returns the fractional width in text eliding

ui/gfx/platform_font_mac.mm

Index: ui/gfx/platform_font_mac.mm
diff --git a/ui/gfx/platform_font_mac.mm b/ui/gfx/platform_font_mac.mm
index c75bf66f0a0f0912d2d4e0aadbb342fe2e9b047e..1e12e0ba9d488a43e1ec3c76af4b9c3d1179a48a 100644
--- a/ui/gfx/platform_font_mac.mm
+++ b/ui/gfx/platform_font_mac.mm
@@ -63,16 +63,16 @@ int PlatformFontMac::GetCapHeight() const {
   return cap_height_;
 }
 
-int PlatformFontMac::GetAverageCharacterWidth() const {
+float PlatformFontMac::GetAverageCharacterWidth() const {
   return average_width_;
 }
 
-int PlatformFontMac::GetStringWidth(const base::string16& text) const {
+float PlatformFontMac::GetStringWidth(const base::string16& text) const {
   return Canvas::GetStringWidth(text,
                                 Font(const_cast<PlatformFontMac*>(this)));
 }
 
-int PlatformFontMac::GetExpectedTextWidth(int length) const {
+float PlatformFontMac::GetExpectedTextWidth(int length) const {
   return length * average_width_;
 }