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

sandbox/linux/services/syscall_wrappers_unittest.cc

Index: sandbox/linux/services/syscall_wrappers_unittest.cc
diff --git a/sandbox/linux/services/syscall_wrappers_unittest.cc b/sandbox/linux/services/syscall_wrappers_unittest.cc
index bac3881ae06c11809b6fe0ebd4b9db46cb883016..a8b48fe586f04677a4add441b47a5dd2f42986d4 100644
--- a/sandbox/linux/services/syscall_wrappers_unittest.cc
+++ b/sandbox/linux/services/syscall_wrappers_unittest.cc
@@ -60,35 +60,6 @@ TEST(SyscallWrappers, CloneChildSettid) {
   EXPECT_EQ(kSuccessExit, WEXITSTATUS(status));
 }
 
-TEST(SyscallWrappers, ForkWithFlagsUpdatesPidCache) {
-  // The libc clone function, which allows ForkWithFlags to keep the pid cache
-  // up to date, does not work on Valgrind.
-  if (IsRunningOnValgrind()) {
-    return;
-  }
-
-  // Warm up the libc pid cache, if there is one.
-  ASSERT_EQ(sys_getpid(), getpid());
-
-  pid_t ctid = 0;
-  pid_t pid = ForkWithFlags(CLONE_CHILD_SETTID | SIGCHLD, nullptr, &ctid);
-
-  const int kSuccessExit = 0;
-  if (0 == pid) {
-    // In child.  Check both the raw getpid syscall and the libc getpid wrapper
-    // (which may rely on a pid cache).
-    if (sys_getpid() == ctid && getpid() == ctid)
-      _exit(kSuccessExit);
-    _exit(1);
-  }
-
-  ASSERT_NE(-1, pid);
-  int status = 0;
-  ASSERT_EQ(pid, HANDLE_EINTR(waitpid(pid, &status, 0)));
-  ASSERT_TRUE(WIFEXITED(status));
-  EXPECT_EQ(kSuccessExit, WEXITSTATUS(status));
-}
-
 }  // namespace
 
 }  // namespace sandbox