Clean-up: Renames gfx::Font's methods and removes its obsolete methods.

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 877507eb47bce1f22de31973198fa728056a7f23..53e3013170cba2145ca693431bc17d1cc89562d3 100644
--- a/ui/gfx/platform_font_mac.mm
+++ b/ui/gfx/platform_font_mac.mm
@@ -105,15 +105,6 @@ int PlatformFontMac::GetCapHeight() const {
   return cap_height_;
 }
 
-int PlatformFontMac::GetAverageCharacterWidth() const {
-  return average_width_;
-}
-
-int PlatformFontMac::GetStringWidth(const base::string16& text) const {
-  return Canvas::GetStringWidth(text,
-                                Font(const_cast<PlatformFontMac*>(this)));
-}
-
 int PlatformFontMac::GetExpectedTextWidth(int length) const {
   return length * average_width_;
 }