null_cb           820 base/bind_unittest.cc   base::Callback<void(int)> null_cb;
null_cb           821 base/bind_unittest.cc   ASSERT_TRUE(null_cb.is_null());
null_cb           822 base/bind_unittest.cc   EXPECT_DEATH(base::Bind(null_cb, 42), "");
null_cb           231 ipc/ipc_send_fds_test.cc       null_listener_(base::Bind(&null_cb), 0) {