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

chrome/browser/renderer_host/browser_render_process_host.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.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "chrome/browser/renderer_host/browser_render_process_host.h"
 
 #include <algorithm>
@@ skipping 256 matching lines @@
   scoped_refptr<ResourceMessageFilter> resource_message_filter =
       new ResourceMessageFilter(g_browser_process->resource_dispatcher_host(),
                                 id(),
                                 audio_renderer_host_.get(),
                                 PluginService::GetInstance(),
                                 g_browser_process->print_job_manager(),
                                 profile(),
                                 widget_helper_,
                                 request_context);
 
-  std::wstring renderer_prefix;
+  CommandLine::StringType renderer_prefix;
 #if defined(OS_POSIX)
   // A command prefix is something prepended to the command line of the spawned
   // process. It is supported only on POSIX systems.
   const CommandLine& browser_command_line = *CommandLine::ForCurrentProcess();
   renderer_prefix =
-      browser_command_line.GetSwitchValue(switches::kRendererCmdPrefix);
+      browser_command_line.GetSwitchValueNative(switches::kRendererCmdPrefix);
 #endif  // defined(OS_POSIX)
 
   // Find the renderer before creating the channel so if this fails early we
   // return without creating the channel.
-  FilePath renderer_path = ChildProcessHost::GetChildPath(
-      renderer_prefix.empty());
+  FilePath renderer_path =
+      ChildProcessHost::GetChildPath(renderer_prefix.empty());
   if (renderer_path.empty())
     return false;
 
   // Setup the IPC channel.
   const std::string channel_id =
       ChildProcessInfo::GenerateRandomChannelID(this);
   channel_.reset(
       new IPC::SyncChannel(channel_id, IPC::Channel::MODE_SERVER, this,
                            resource_message_filter,
                            io_thread->message_loop(), true,
@@ skipping 766 matching lines @@
         IPC::InvalidPlatformFileForTransit(),
         std::vector<std::string>(),
         std::string(),
         false));
   }
 }
 
 void BrowserRenderProcessHost::EnableAutoSpellCorrect(bool enable) {
   Send(new ViewMsg_SpellChecker_EnableAutoSpellCorrect(enable));
 }