Add the ability to change directories before execing.

base/process/launch_posix.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 "base/process/launch.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <sched.h>
@@ skipping 498 matching lines @@
 #endif
     if (!options.allow_new_privs) {
       if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) && errno != EINVAL) {
         // Only log if the error is not EINVAL (i.e. not supported).
         RAW_LOG(FATAL, "prctl(PR_SET_NO_NEW_PRIVS) failed");
       }
     }
 #endif
 
 #if defined(OS_POSIX)
+    if (!options.current_directory.empty()) {
+      RAW_CHECK(chdir(options.current_directory.value().c_str()) == 0);

[jln (very slow on Chromium), 2015/02/03 02:07:53]

Sorry I didn't comment on that before: you need to do the c_str() conversion
prefork to be async safe.

[rickyz (no longer on Chrome), 2015/02/03 02:17:56]

Sure, I moved another c_str caller up as well.

+    }
+
     if (options.pre_exec_delegate != nullptr) {
       options.pre_exec_delegate->RunAsyncSafe();
     }
 #endif
 
     for (size_t i = 0; i < argv.size(); i++)
       argv_cstr[i] = const_cast<char*>(argv[i].c_str());
     argv_cstr[argv.size()] = NULL;
     execvp(argv_cstr[0], argv_cstr.get());
 
@@ skipping 230 matching lines @@
   jmp_buf env;
   if (setjmp(env) == 0) {
     return CloneAndLongjmpInChild(flags, ptid, ctid, &env);
   }
 
   return 0;
 }
 #endif  // defined(OS_LINUX)
 
 }  // namespace base