Remove all uses of EmptyString16(), EmptyWString(), and EmptyGURL(), and thei...

base/string_util.h

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // This file defines utility functions for working with strings.
 
 #ifndef BASE_STRING_UTIL_H_
 #define BASE_STRING_UTIL_H_
 
 #include <stdarg.h>   // va_list
@@ skipping 103 matching lines @@
 }  // namespace base
 
 #if defined(OS_WIN)
 #include "base/string_util_win.h"
 #elif defined(OS_POSIX)
 #include "base/string_util_posix.h"
 #else
 #error Define string operations appropriately for your platform
 #endif
 
-// Returns a reference to a globally unique empty string that functions can
-// return.  Use this to avoid static construction of strings, not to replace
-// any and all uses of "std::string()" as nicer-looking sugar.
-// These functions are threadsafe.
+// These threadsafe functions return references to globally unique empty
+// strings.
+//
+// DO NOT USE THESE AS A GENERAL-PURPOSE SUBSTITUTE FOR DEFAULT CONSTRUCTORS.
+// There is only one case where you should use these: functions which need to
+// return a string by reference (e.g. as a class member accessor), and don't
+// have an empty string to use (e.g. in an error case).  These should not be
+// used as initializers, function arguments, or return values for functions
+// which return by value or outparam.
 const std::string& EmptyString();
 const std::wstring& EmptyWString();
 const string16& EmptyString16();
 
 extern const wchar_t kWhitespaceWide[];
 extern const char16 kWhitespaceUTF16[];
 extern const char kWhitespaceASCII[];
 
 extern const char kUtf8ByteOrderMark[];
 
@@ skipping 505 matching lines @@
 #elif defined(WCHAR_T_IS_UTF32)
   typedef uint32 Unsigned;
 #endif
 };
 template<>
 struct ToUnsigned<short> {
   typedef unsigned short Unsigned;
 };
 
 #endif  // BASE_STRING_UTIL_H_