Move |PlatformFont::GetStringWidth()| implementation up into font.cc directly.

ui/gfx/platform_font_mac.mm

Index: ui/gfx/platform_font_mac.mm
===================================================================
--- ui/gfx/platform_font_mac.mm	(revision 118837)
+++ ui/gfx/platform_font_mac.mm	(working copy)
@@ -10,7 +10,6 @@
 #include "base/memory/scoped_nsobject.h"
 #include "base/sys_string_conversions.h"
 #include "base/utf_string_conversions.h"
-#include "ui/gfx/canvas_skia.h"
 #include "ui/gfx/font.h"
 
 namespace gfx {
@@ -56,13 +55,6 @@
   return average_width_;
 }
 
-int PlatformFontMac::GetStringWidth(const string16& text) const {
-  int width = 0, height = 0;
-  CanvasSkia::SizeStringInt(text, Font(const_cast<PlatformFontMac*>(this)),
-                            &width, &height, gfx::Canvas::NO_ELLIPSIS);
-  return width;
-}
-
 int PlatformFontMac::GetExpectedTextWidth(int length) const {
   return length * average_width_;
 }