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

chrome/test/ui/ui_test.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 "chrome/test/ui/ui_test.h"
 
 #if defined(OS_POSIX)
 #include <signal.h>
 #include <sys/types.h>
 #endif
@@ skipping 1191 matching lines @@
                                  wait,
                                  !show_window_,
                                  process);
 #elif defined(OS_POSIX)
   // Sometimes one needs to run the browser under a special environment
   // (e.g. valgrind) without also running the test harness (e.g. python)
   // under the special environment.  Provide a way to wrap the browser
   // commandline with a special prefix to invoke the special environment.
   const char* browser_wrapper = getenv("BROWSER_WRAPPER");
   if (browser_wrapper) {
-    command_line.PrependWrapper(ASCIIToWide(browser_wrapper));
+    command_line.PrependWrapper(browser_wrapper);
     LOG(INFO) << "BROWSER_WRAPPER was set, prefixing command_line with "
               << browser_wrapper;
   }
 
   bool started = base::LaunchApp(command_line.argv(),
                                  server_->fds_to_map(),
                                  wait,
                                  process);
 #endif
 
@@ skipping 298 matching lines @@
                      test_info->name());
   }
   UITestBase::SetUp();
   PlatformTest::SetUp();
 }
 
 void UITest::TearDown() {
   UITestBase::TearDown();
   PlatformTest::TearDown();
 }