Move ForkWithFlags from sandbox/ to base/ and plug it into LaunchProcess.

base/process/process.h

 // Copyright (c) 2011 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.
 
 #ifndef BASE_PROCESS_PROCESS_PROCESS_H_
 #define BASE_PROCESS_PROCESS_PROCESS_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/move.h"
@@ skipping 94 matching lines @@
 
  private:
 #if defined(OS_WIN)
   bool is_current_process_;
   win::ScopedHandle process_;
 #else
   ProcessHandle process_;
 #endif
 };
 
+#if defined(OS_LINUX)
+// A wrapper for clone with fork-like behavior, meaning that it returns the
+// child's pid in the parent and 0 in the child. |flags|, |ptid|, and |ctid| are
+// as in the clone system call (the CLONE_VM flag is not supported).
+//
+// This function uses the libc clone wrapper (which updates libc's pid cache)
+// internally, so callers may expect things like getpid() to work correctly
+// after in both the child and parent. An exception is when this code is run
+// under Valgrind. Valgrind does not support the libc clone wrapper, so the libc
+// pid cache may be incorrect after this function is called under Valgrind.
+BASE_EXPORT pid_t ForkWithFlags(unsigned long flags, pid_t* ptid, pid_t* ctid);

[jln (very slow on Chromium), 2015/01/06 00:22:31]

It may be useful to warn about the usual fork() issues, such as the fact that
forking with threads requires a lot of care (and typically doing an execve()
soon).

[rickyz (no longer on Chrome), 2015/01/06 02:45:37]

Done.

+#endif
+
 }  // namespace base
 
 #endif  // BASE_PROCESS_PROCESS_PROCESS_H_