VCD: Fix DCHECK failure when stopping streaming

Bug: b/175520499
Test: Chrome won't crash after closing page while streaming
Change-Id: I28d0c34a0ee8e0cd25fbe5c65e7c860d6f6bb00d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2589413
Auto-Submit: Wei Lee <wtlee@chromium.org>
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Wei Lee <wtlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836925}

media/capture/video/chromeos/video_capture_device_chromeos_delegate.cc

@@ -181,7 +181,7 @@ void VideoCaptureDeviceChromeOSDelegate::AllocateAndStart(
 void VideoCaptureDeviceChromeOSDelegate::StopAndDeAllocate(
     ClientType client_type) {
   DCHECK(capture_task_runner_->BelongsToCurrentThread());
-  DCHECK(!camera_device_delegate_);
+  DCHECK(camera_device_delegate_);
   device_context_->RemoveClient(client_type);
   if (!HasDeviceClient()) {
     CloseDevice(base::UnguessableToken());