Continue to clean c_str() calls.

components/nacl/zygote/nacl_fork_delegate_linux.cc

 // Copyright (c) 2012 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 "components/nacl/zygote/nacl_fork_delegate_linux.h"
 
 #include <signal.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <sys/resource.h>
@@ skipping 441 matching lines @@
     pass_through_vars = base::SplitString(
         pass_through_string, std::string(1, kNaClEnvPassthroughDelimiter),
         base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
   }
   pass_through_vars.push_back(kNaClExeStderr);
   pass_through_vars.push_back(kNaClExeStdout);
   pass_through_vars.push_back(kNaClVerbosity);
   pass_through_vars.push_back(sandbox::kSandboxEnvironmentApiRequest);
   for (size_t i = 0; i < pass_through_vars.size(); ++i) {
     std::string temp;
-    if (env->GetVar(pass_through_vars[i].c_str(), &temp))
+    if (env->GetVar(pass_through_vars[i], &temp))
       options->environ[pass_through_vars[i]] = temp;
   }
 }
 
 }  // namespace nacl