Fix mac after https://codereview.chromium.org/1419623003/

minidump/minidump_string_writer.h

Index: minidump/minidump_string_writer.h
diff --git a/minidump/minidump_string_writer.h b/minidump/minidump_string_writer.h
index 5b82bfd2b98474320eb1c94db61cec8108cbea2c..ec57179ee9a092e6d9fcedb121ca565badbed248 100644
--- a/minidump/minidump_string_writer.h
+++ b/minidump/minidump_string_writer.h
@@ -99,13 +99,6 @@ class MinidumpUTF16StringWriter final
   //! \note Valid in #kStateMutable.
   void SetUTF8(const std::string& string_utf8);
 
-  //! \brief Sets the given UTF-16 string as the string to be written.
-  //!
-  //! \note Valid in #kStateMutable.
-  void SetUTF16(const base::string16& string_utf16) {
-    set_string(string_utf16);
-  }
-
  private:
   DISALLOW_COPY_AND_ASSIGN(MinidumpUTF16StringWriter);
 };