net/socket: Replace QuitWhenIdleClosure() with QuitClosure()

Method QuitClosure() provides more deterministic behaviour than
QuitWhenIdleClosure().

R=wez@chromium.org

Change-Id: I523bae5be0a176d5e6239573f20c78894a43e352
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2236398Reviewed-by: Wez <wez@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780268}

net/socket/client_socket_pool_base_unittest.cc

@@ -4227,7 +4227,7 @@ TEST_F(ClientSocketPoolBaseTest, PreconnectWithoutBackupJob) {
   base::RunLoop loop;
   connect_job_factory_->set_job_type(TestConnectJob::kMockPendingJob);
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, loop.QuitWhenIdleClosure(), base::TimeDelta::FromSeconds(1));
+      FROM_HERE, loop.QuitClosure(), base::TimeDelta::FromSeconds(1));
   loop.Run();
   EXPECT_FALSE(pool_->HasGroupForTesting(TestGroupId("a")));
 }