VCD: Initialize active client observer

This CL fixes an issue where the scoped_ref base::ObserverListThreadSafe
isn't initialized, causing chrome to crash immediately following
CameraHalDispatcherImpl::AddActiveClientObserver().
It also adds a unittest to make sure the observer works.

Bug: 1155159
Test: Create an observer in camera_hal_delegate.cc and verify that the
observer is registered and receives updates. \
  (DUT) $ capture_unittests --gtest_filter='*Dispatcher*'

Change-Id: I54a8a77a2b48eb328ca2c1f0a2fb3ce057f66b31
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2575297Reviewed-by: Wei Lee <wtlee@chromium.org>
Commit-Queue: Wei Lee <wtlee@chromium.org>
Auto-Submit: Jasmine Chen <lnishan@google.com>
Cr-Commit-Position: refs/heads/master@{#834553}

media/capture/video/chromeos/camera_hal_dispatcher_impl.cc

@@ -216,7 +216,9 @@ void CameraHalDispatcherImpl::UnregisterPluginVmToken(
 CameraHalDispatcherImpl::CameraHalDispatcherImpl()
     : proxy_thread_("CameraProxyThread"),
       blocking_io_thread_("CameraBlockingIOThread"),
-      camera_hal_server_callbacks_(this) {
+      camera_hal_server_callbacks_(this),
+      active_client_observers_(
+          new base::ObserverListThreadSafe<CameraActiveClientObserver>()) {
   // This event is for adding camera category to categories list.
   TRACE_EVENT0("camera", "CameraHalDispatcherImpl");
   base::trace_event::TraceLog::GetInstance()->AddEnabledStateObserver(this);

media/capture/video/chromeos/camera_hal_dispatcher_impl_unittest.cc

@@ -76,6 +76,16 @@ class MockCameraHalClient : public cros::mojom::CameraHalClient {
   DISALLOW_COPY_AND_ASSIGN(MockCameraHalClient);
 };
 
+class MockCameraActiveClientObserver : public CameraActiveClientObserver {
+ public:
+  void OnActiveClientChange(cros::mojom::CameraClientType type,
+                            bool is_active) override {
+    DoOnActiveClientChange(type, is_active);
+  }
+  MOCK_METHOD2(DoOnActiveClientChange,
+               void(cros::mojom::CameraClientType, bool));
+};
+
 }  // namespace
 
 class CameraHalDispatcherImplTest : public ::testing::Test {
@@ -253,4 +263,32 @@ TEST_F(CameraHalDispatcherImplTest, ClientConnectionError) {
   DoLoop();
 }
 
+// Test that CameraHalDispatcherImpl correctly fires CameraActiveClientObserver
+// when a camera device is opened or closed by a client.
+TEST_F(CameraHalDispatcherImplTest, CameraActiveClientObserverTest) {
+  MockCameraActiveClientObserver observer;
+  dispatcher_->AddActiveClientObserver(&observer);
+
+  EXPECT_CALL(observer, DoOnActiveClientChange(
+                            cros::mojom::CameraClientType::TESTING, true))
+      .Times(1)
+      .WillOnce(
+          InvokeWithoutArgs(this, &CameraHalDispatcherImplTest::QuitRunLoop));
+  dispatcher_->CameraDeviceActivityChange(
+      /*camera_id=*/0, /*opened=*/true, cros::mojom::CameraClientType::TESTING);
+
+  DoLoop();
+
+  EXPECT_CALL(observer, DoOnActiveClientChange(
+                            cros::mojom::CameraClientType::TESTING, false))
+      .Times(1)
+      .WillOnce(
+          InvokeWithoutArgs(this, &CameraHalDispatcherImplTest::QuitRunLoop));
+  dispatcher_->CameraDeviceActivityChange(
+      /*camera_id=*/0, /*opened=*/false,
+      cros::mojom::CameraClientType::TESTING);
+
+  DoLoop();
+}
+
 }  // namespace media