ui/gfx: Use base::string16 now that string16 was moved into base namespace.

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 7da2ec9f5d1547bb584650a3b979d23cc5bcd662..eff0c0f0c01e71859255f7c368763fa607ce45c4 100644
--- a/ui/gfx/platform_font_mac.mm
+++ b/ui/gfx/platform_font_mac.mm
@@ -63,7 +63,7 @@ int PlatformFontMac::GetAverageCharacterWidth() const {
   return average_width_;
 }
 
-int PlatformFontMac::GetStringWidth(const string16& text) const {
+int PlatformFontMac::GetStringWidth(const base::string16& text) const {
   return Canvas::GetStringWidth(text,
                                 Font(const_cast<PlatformFontMac*>(this)));
 }