Add the ability to run a callback between fork and exec.

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 <signal.h>
@@ skipping 430 matching lines @@
 #define PR_SET_NO_NEW_PRIVS 38
 #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.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());
 
     RAW_LOG(ERROR, "LaunchProcess: failed to execvp:");
     RAW_LOG(ERROR, argv_cstr[0]);
     _exit(127);
   } else {
     // Parent process
@@ skipping 203 matching lines @@
                               std::string* output,
                               int* exit_code) {
   // Run |execve()| with the current environment and store "unlimited" data.
   GetAppOutputInternalResult result = GetAppOutputInternal(
       cl.argv(), NULL, output, std::numeric_limits<std::size_t>::max(), true,
       exit_code);
   return result == EXECUTE_SUCCESS;
 }
 
 }  // namespace base