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

base/command_line.cc

 // 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.
 
 #include "base/command_line.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <shellapi.h>
 #elif defined(OS_POSIX)
@@ skipping 414 matching lines @@
   // Verify include_program is used correctly.
   // Logic could be shorter but this is clearer.
   DCHECK_EQ(include_program, !other.GetProgram().empty());
   command_line_string_ += L" " + other.command_line_string_;
   std::map<std::string, StringType>::const_iterator i;
   for (i = other.switches_.begin(); i != other.switches_.end(); ++i)
     switches_[i->first] = i->second;
 }
 
 void CommandLine::PrependWrapper(const std::wstring& wrapper) {
+  if (wrapper.empty())
+    return;
   // The wrapper may have embedded arguments (like "gdb --args"). In this case,
   // we don't pretend to do anything fancy, we just split on spaces.
   std::vector<std::wstring> wrapper_and_args;
   SplitString(wrapper, ' ', &wrapper_and_args);
   program_ = wrapper_and_args[0];
   command_line_string_ = wrapper + L" " + command_line_string_;
 }
 
 #elif defined(OS_POSIX)
 void CommandLine::AppendSwitch(const std::string& switch_string) {
@@ skipping 23 matching lines @@
   // Logic could be shorter but this is clearer.
   DCHECK_EQ(include_program, !other.GetProgram().empty());
   size_t first_arg = include_program ? 0 : 1;
   for (size_t i = first_arg; i < other.argv_.size(); ++i)
     argv_.push_back(other.argv_[i]);
   std::map<std::string, StringType>::const_iterator i;
   for (i = other.switches_.begin(); i != other.switches_.end(); ++i)
     switches_[i->first] = i->second;
 }
 
-void CommandLine::PrependWrapper(const std::wstring& wrapper_wide) {
+void CommandLine::PrependWrapper(const std::string& wrapper) {
   // The wrapper may have embedded arguments (like "gdb --args"). In this case,
   // we don't pretend to do anything fancy, we just split on spaces.
-  const std::string wrapper = base::SysWideToNativeMB(wrapper_wide);
   std::vector<std::string> wrapper_and_args;
   SplitString(wrapper, ' ', &wrapper_and_args);
   argv_.insert(argv_.begin(), wrapper_and_args.begin(), wrapper_and_args.end());
 }
 
 #endif
 
 void CommandLine::AppendSwitchPath(const std::string& switch_string,
                                    const FilePath& path) {
   AppendSwitchNative(switch_string, path.value());
 }
 
 void CommandLine::CopySwitchesFrom(const CommandLine& source,
                                    const char* const switches[],
                                    size_t count) {
   for (size_t i = 0; i < count; ++i) {
     if (source.HasSwitch(switches[i])) {
       StringType value = source.GetSwitchValueNative(switches[i]);
       AppendSwitchNative(switches[i], value);
     }
   }
 }
 
 // private
 CommandLine::CommandLine() {
 }