login: add a test for reentrancy of ArcInstanceStopped event

In this change we're adding a test that simulates the same condition
that was addressed in https://crrev.com/c/2381050 i.e. we ensure that
ArcInstanceStopped is not called on new instances of arc_container_client_adapter
if they're created during handling of ArcInstanceStopped event.

BUG=b:164816080
TEST=components_unittests --gtest_filter='ArcContainerClientAdapterTest*'
TEST=revert the fix and ensure that the test fails

Change-Id: Ibe4911664be8b81a16c6c25a282121f4d83323bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2459528
Commit-Queue: Muhammad Hasan Khan <mhasank@chromium.org>
Reviewed-by: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817065}

components/arc/BUILD.gn

@@ -397,6 +397,7 @@ source_set("unit_tests") {
     "pay/arc_payment_app_bridge_unittest.cc",
     "power/arc_power_bridge_unittest.cc",
     "property/arc_property_bridge_unittest.cc",
+    "session/arc_container_client_adapter_unittest.cc",
     "session/arc_data_remover_unittest.cc",
     "session/arc_property_util_unittest.cc",
     "session/arc_session_impl_unittest.cc",

components/arc/session/arc_container_client_adapter_unittest.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <memory>
+
+#include "base/callback_helpers.h"
+#include "chromeos/dbus/session_manager/fake_session_manager_client.h"
+#include "components/arc/session/arc_container_client_adapter.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace arc {
+
+class ArcContainerClientAdapterTest : public testing::Test {
+ public:
+  ArcContainerClientAdapterTest() = default;
+  ~ArcContainerClientAdapterTest() override = default;
+  ArcContainerClientAdapterTest(const ArcContainerClientAdapterTest&) = delete;
+  ArcContainerClientAdapterTest& operator=(
+      const ArcContainerClientAdapterTest&) = delete;
+
+  void SetUp() override {
+    chromeos::SessionManagerClient::InitializeFake();
+    client_adapter_ = CreateArcContainerClientAdapter();
+  }
+
+  void TearDown() override {
+    client_adapter_ = nullptr;
+    chromeos::SessionManagerClient::Shutdown();
+  }
+
+ protected:
+  ArcClientAdapter* client_adapter() { return client_adapter_.get(); }
+
+ private:
+  std::unique_ptr<ArcClientAdapter> client_adapter_;
+};
+
+// b/164816080 This test ensures that a new container instance that is
+// created while handling the shutting down of the previous instance,
+// doesn't incorrectly receive the shutdown event as well.
+TEST_F(ArcContainerClientAdapterTest,
+       DoesNotGetArcInstanceStoppedOnNestedInstance) {
+  class Observer : public ArcClientAdapter::Observer {
+   public:
+    explicit Observer(Observer* child_observer)
+        : child_observer_(child_observer) {}
+    Observer(const Observer&) = delete;
+    Observer& operator=(const Observer&) = delete;
+
+    ~Observer() override {
+      if (child_observer_ && nested_client_adapter_)
+        nested_client_adapter_->RemoveObserver(child_observer_);
+    }
+
+    bool stopped_called() const { return stopped_called_; }
+
+    // ArcClientAdapter::Observer:
+    void ArcInstanceStopped() override {
+      stopped_called_ = true;
+
+      if (child_observer_) {
+        nested_client_adapter_ = CreateArcContainerClientAdapter();
+        nested_client_adapter_->AddObserver(child_observer_);
+      }
+    }
+
+   private:
+    Observer* const child_observer_;
+    std::unique_ptr<ArcClientAdapter> nested_client_adapter_;
+    bool stopped_called_ = false;
+  };
+
+  Observer child_observer(nullptr);
+  Observer parent_observer(&child_observer);
+  client_adapter()->AddObserver(&parent_observer);
+  base::ScopedClosureRunner teardown(base::BindOnce(
+      [](ArcClientAdapter* client_adapter, Observer* parent_observer) {
+        client_adapter->RemoveObserver(parent_observer);
+      },
+      client_adapter(), &parent_observer));
+
+  chromeos::FakeSessionManagerClient::Get()->NotifyArcInstanceStopped();
+
+  EXPECT_TRUE(parent_observer.stopped_called());
+  EXPECT_FALSE(child_observer.stopped_called());
+}
+
+}  // namespace arc

components/arc/session/arc_session_runner.cc

@@ -258,8 +258,6 @@ void ArcSessionRunner::SetRestartDelayForTesting(
   restart_delay_ = restart_delay;
 }
 
-// TODO(b/164816080) add a test to ensure OnSessionStopped is not called
-// when starting ARC session after failed attempt
 void ArcSessionRunner::StartArcSession() {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
   DCHECK(!restart_timer_.IsRunning());