[MediaStreamDeviceObserver] Reset the receiver before Bind().

Reset the receiver before Bind(), in case it was already bound, to avoid
running into Bind()'s internal DCHECK that expects the receiver to not
be bound.

Also add a test verifying that OnDeviceChanged() behaves as expected
after rebind.

Bug: 1093728
Change-Id: Ic964902d3f3af3e3c6963633c13b069ecb344d96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250040Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Marina Ciocea <marinaciocea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779731}

third_party/blink/renderer/modules/mediastream/media_stream_device_observer.cc

@@ -132,6 +132,7 @@ void MediaStreamDeviceObserver::OnDeviceChanged(
 
 void MediaStreamDeviceObserver::BindMediaStreamDeviceObserverReceiver(
     mojo::PendingReceiver<mojom::blink::MediaStreamDeviceObserver> receiver) {
+  receiver_.reset();
   receiver_.Bind(std::move(receiver));
 }
 

third_party/blink/renderer/modules/mediastream/media_stream_device_observer.h

@@ -64,6 +64,8 @@ class MODULES_EXPORT MediaStreamDeviceObserver
                            GetNonScreenCaptureDevices);
   FRIEND_TEST_ALL_PREFIXES(MediaStreamDeviceObserverTest, OnDeviceStopped);
   FRIEND_TEST_ALL_PREFIXES(MediaStreamDeviceObserverTest, OnDeviceChanged);
+  FRIEND_TEST_ALL_PREFIXES(MediaStreamDeviceObserverTest,
+                           OnDeviceChangedChangesDeviceAfterRebind);
 
   // Private class for keeping track of opened devices and who have
   // opened it.

third_party/blink/renderer/modules/mediastream/media_stream_device_observer_test.cc

@@ -11,8 +11,10 @@
 
 #include "base/bind.h"
 #include "base/run_loop.h"
+#include "mojo/public/cpp/bindings/remote.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/blink/public/common/mediastream/media_stream_request.h"
+#include "third_party/blink/public/mojom/mediastream/media_stream.mojom-blink.h"
 #include "third_party/blink/renderer/modules/mediastream/mock_mojo_media_stream_dispatcher_host.h"
 
 namespace blink {
@@ -157,4 +159,49 @@ TEST_F(MediaStreamDeviceObserverTest, OnDeviceChanged) {
   EXPECT_EQ(observer_->label_stream_map_.size(), 0u);
 }
 
+TEST_F(MediaStreamDeviceObserverTest, OnDeviceChangedChangesDeviceAfterRebind) {
+  const String kStreamLabel = "stream_label";
+  const std::string kDeviceName = "Video Device";
+  const blink::mojom::MediaStreamType kDeviceType =
+      blink::mojom::MediaStreamType::DEVICE_VIDEO_CAPTURE;
+
+  // Add a device to the |observer_|, to be changed using OnChangedDevice().
+  blink::MediaStreamDevice initial_device(kDeviceType, "initial_device",
+                                          kDeviceName);
+  observer_->AddStream(kStreamLabel, initial_device);
+
+  // Call the |observer_|'s bind callback and check that its internal
+  // |receiver_| is bound.
+  mojo::Remote<mojom::blink::MediaStreamDeviceObserver> remote_observer;
+  EXPECT_FALSE(observer_->receiver_.is_bound());
+  observer_->BindMediaStreamDeviceObserverReceiver(
+      remote_observer.BindNewPipeAndPassReceiver());
+  EXPECT_TRUE(observer_->receiver_.is_bound());
+
+  // Send an OnDeviceChanged() message using the remote mojo pipe, and verify
+  // that the device is changed.
+  blink::MediaStreamDevice changed_device =
+      blink::MediaStreamDevice(kDeviceType, "video_device-123", kDeviceName);
+  remote_observer->OnDeviceChanged(kStreamLabel, initial_device,
+                                   changed_device);
+  base::RunLoop().RunUntilIdle();
+  blink::MediaStreamDevices video_devices =
+      observer_->GetNonScreenCaptureDevices();
+  ASSERT_EQ(video_devices.size(), 1u);
+  EXPECT_EQ(video_devices[0].id, "video_device-123");
+
+  // Reset the remote end of the mojo pipe, then rebind it, and verify that
+  // OnDeviceChanged() changes the device after rebind.
+  remote_observer.reset();
+  observer_->BindMediaStreamDeviceObserverReceiver(
+      remote_observer.BindNewPipeAndPassReceiver());
+  remote_observer->OnDeviceChanged(
+      kStreamLabel, changed_device,
+      blink::MediaStreamDevice(kDeviceType, "video_device-456", kDeviceName));
+  base::RunLoop().RunUntilIdle();
+  video_devices = observer_->GetNonScreenCaptureDevices();
+  ASSERT_EQ(video_devices.size(), 1u);
+  EXPECT_EQ(video_devices[0].id, "video_device-456");
+}
+
 }  // namespace blink