Update from https://crrev.com/312600

base/process/launch.h

Index: base/process/launch.h
diff --git a/base/process/launch.h b/base/process/launch.h
index eca4f8f7a44eeb1af2b0625dff6bc3f0b32b60d3..de1bc0af821f2bb54160b8fda873093388c811d9 100644
--- a/base/process/launch.h
+++ b/base/process/launch.h
@@ -291,6 +291,25 @@ void ReplaceBootstrapPort(const std::string& replacement_bootstrap_name);
 // binary. This should not be called in production/released code.
 BASE_EXPORT LaunchOptions LaunchOptionsForTest();
 
+#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.
+//
+// As with fork(), callers should be extremely careful when calling this while
+// multiple threads are running, since at the time the fork happened, the
+// threads could have been in any state (potentially holding locks, etc.).
+// Callers should most likely call execve() in the child soon after calling
+// this.
+BASE_EXPORT pid_t ForkWithFlags(unsigned long flags, pid_t* ptid, pid_t* ctid);
+#endif
+
 }  // namespace base
 
 #endif  // BASE_PROCESS_LAUNCH_H_