PrependWrapper is platform-specific, so it should take a platform string.

base/command_line.h

 // Copyright (c) 2006-2008 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 class works with command lines: building and parsing.
 // Switches can optionally have a value attached using an equals sign,
 // as in "-switch=value".  Arguments that aren't prefixed with a
 // switch prefix are saved as extra arguments.  An argument of "--"
 // will terminate switch parsing, causing everything after to be
 // considered as extra arguments.
@@ skipping 155 matching lines @@
                          const std::string& value);
 
   // Append a loose value to the command line.
   void AppendLooseValue(const std::wstring& value);
 
   // Append the arguments from another command line to this one.
   // If |include_program| is true, include |other|'s program as well.
   void AppendArguments(const CommandLine& other,
                        bool include_program);
 
-  // On POSIX systems it's common to run processes via a wrapper (like
-  // "valgrind" or "gdb --args").
-  void PrependWrapper(const std::wstring& wrapper);
+  // Insert a command before the current command.  Common for debuggers,
+  // like "valgrind" or "gdb --args".
+  void PrependWrapper(const StringType& wrapper);
 
   // Copy a set of switches (and their values, if any) from another command
   // line.  Commonly used when launching a subprocess.
   void CopySwitchesFrom(const CommandLine& source, const char* const switches[],
                         size_t count);
 
  private:
   friend class InProcessBrowserTest;
 
   CommandLine();
@@ skipping 34 matching lines @@
   std::vector<StringType> args_;
 
   // We allow copy constructors, because a common pattern is to grab a
   // copy of the current process's command line and then add some
   // flags to it.  E.g.:
   //   CommandLine cl(*CommandLine::ForCurrentProcess());
   //   cl.AppendSwitch(...);
 };
 
 #endif  // BASE_COMMAND_LINE_H_