Fix and re-enable IPCMojoBootstrapTest.ReceiveEmptyMessage

Lets the test run longer (i.e. until the child actually closes its
Channel) before asserting that we receive a message from the child.

Bug: 821254
Change-Id: I629d994baf5655899dbd95177b997b97fd112e32
Reviewed-on: https://chromium-review.googlesource.com/981445
Commit-Queue: Ken Rockot <rockot@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545972}

ipc/ipc_mojo_bootstrap_unittest.cc

@@ -11,6 +11,7 @@
 #include "base/files/file.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/test/bind_test_util.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "ipc/ipc.mojom.h"
@@ -96,6 +97,12 @@ class PeerPidReceiver : public IPC::mojom::Channel {
 
   int32_t peer_pid() const { return peer_pid_; }
 
+  void RunUntilDisconnect() {
+    base::RunLoop run_loop;
+    binding_.set_connection_error_handler(run_loop.QuitClosure());
+    run_loop.Run();
+  }
+
  private:
   mojo::AssociatedBinding<IPC::mojom::Channel> binding_;
   const base::Closure on_peer_pid_set_;
@@ -130,52 +137,56 @@ TEST_F(IPCMojoBootstrapTest, Connect) {
 
   EXPECT_EQ(kTestClientPid, impl.peer_pid());
 
+  impl.RunUntilDisconnect();
   EXPECT_TRUE(helper_.WaitForChildTestShutdown());
 }
 
-// TODO(https://crbug.com/821254): Fix this test and re-enable it.
-TEST_F(IPCMojoBootstrapTest, DISABLED_ReceiveEmptyMessage) {
+// A long running process that connects to us.
+MULTIPROCESS_TEST_MAIN_WITH_SETUP(
+    IPCMojoBootstrapTestClientTestChildMain,
+    ::mojo::edk::test::MultiprocessTestHelper::ChildSetup) {
   base::MessageLoop message_loop;
   Connection connection(
       IPC::MojoBootstrap::Create(
-          helper_.StartChild("IPCMojoBootstrapTestEmptyMessage"),
-          IPC::Channel::MODE_SERVER, base::ThreadTaskRunnerHandle::Get(),
+          std::move(mojo::edk::test::MultiprocessTestHelper::primordial_pipe),
+          IPC::Channel::MODE_CLIENT, base::ThreadTaskRunnerHandle::Get(),
           base::ThreadTaskRunnerHandle::Get()),
-      kTestServerPid);
+      kTestClientPid);
 
   IPC::mojom::ChannelAssociatedRequest receiver;
   connection.TakeReceiver(&receiver);
 
   base::RunLoop run_loop;
-  PeerPidReceiver impl(std::move(receiver), run_loop.QuitClosure(),
-                       PeerPidReceiver::MessageExpectation::kExpectedInvalid);
+  PeerPidReceiver impl(std::move(receiver), run_loop.QuitClosure());
   run_loop.Run();
 
-  EXPECT_TRUE(helper_.WaitForChildTestShutdown());
+  EXPECT_EQ(kTestServerPid, impl.peer_pid());
+
+  return 0;
 }
 
-// A long running process that connects to us.
-MULTIPROCESS_TEST_MAIN_WITH_SETUP(
-    IPCMojoBootstrapTestClientTestChildMain,
-    ::mojo::edk::test::MultiprocessTestHelper::ChildSetup) {
+TEST_F(IPCMojoBootstrapTest, ReceiveEmptyMessage) {
   base::MessageLoop message_loop;
   Connection connection(
       IPC::MojoBootstrap::Create(
-          std::move(mojo::edk::test::MultiprocessTestHelper::primordial_pipe),
-          IPC::Channel::MODE_CLIENT, base::ThreadTaskRunnerHandle::Get(),
+          helper_.StartChild("IPCMojoBootstrapTestEmptyMessage"),
+          IPC::Channel::MODE_SERVER, base::ThreadTaskRunnerHandle::Get(),
           base::ThreadTaskRunnerHandle::Get()),
-      kTestClientPid);
+      kTestServerPid);
 
   IPC::mojom::ChannelAssociatedRequest receiver;
   connection.TakeReceiver(&receiver);
 
   base::RunLoop run_loop;
-  PeerPidReceiver impl(std::move(receiver), run_loop.QuitClosure());
+  PeerPidReceiver impl(std::move(receiver), run_loop.QuitClosure(),
+                       PeerPidReceiver::MessageExpectation::kExpectedInvalid);
   run_loop.Run();
 
-  EXPECT_EQ(kTestServerPid, impl.peer_pid());
+  // Wait for the Channel to be disconnected so we can reasonably assert that
+  // the child's empty message must have been received before we pass the test.
+  impl.RunUntilDisconnect();
 
-  return 0;
+  EXPECT_TRUE(helper_.WaitForChildTestShutdown());
 }
 
 // A long running process that connects to us.