mac: Fix os_exchange_data_provider_mac.mm.

ui/base/dragdrop/os_exchange_data.h

Index: ui/base/dragdrop/os_exchange_data.h
diff --git a/ui/base/dragdrop/os_exchange_data.h b/ui/base/dragdrop/os_exchange_data.h
index 55e8e5637b99b454bd9a6e813d7c50d108510dc4..6bbf9186f6d3cbb7a1eec8096961d0dbd59bf4c8 100644
--- a/ui/base/dragdrop/os_exchange_data.h
+++ b/ui/base/dragdrop/os_exchange_data.h
@@ -190,6 +190,8 @@ class UI_BASE_EXPORT OSExchangeData {
   // functions return and the result is in the out parameter. If the data does
   // not exist, the out parameter is not touched. The out parameter cannot be
   // NULL.
+  // GetString() returns the plain text representation of the pasteboard
+  // contents.
   bool GetString(base::string16* data) const;
   bool GetURLAndTitle(FilenameToURLPolicy policy,
                       GURL* url,