Fix MediaDevices* tests dependency on BrowserThread globals after ~BrowserThreadImpl().

content/browser/renderer_host/media/media_devices_dispatcher_host_unittest.cc

 // Copyright 2016 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 "content/browser/renderer_host/media/media_devices_dispatcher_host.h"
 
 #include <stddef.h>
 
 #include <memory>
 #include <queue>
@@ skipping 233 matching lines @@
       base::RunLoop().RunUntilIdle();
       host_->UnsubscribeDeviceChangeNotifications(type, subscription_id);
 
       if (has_permission)
         EXPECT_TRUE(DoesContainLabels(changed_devices));
       else
         EXPECT_TRUE(DoesNotContainLabels(changed_devices));
     }
   }
 
-  std::unique_ptr<MediaDevicesDispatcherHost> host_;
+  // The order of these members is important on teardown:
+  // MediaDevicesDispatcherHost expects to be destroyed on the IO thread while
+  // MediaStreamManager expects to be destroyed after the IO thread has been
+  // uninitialized.
   std::unique_ptr<MediaStreamManager> media_stream_manager_;
   content::TestBrowserThreadBundle thread_bundle_;
+  std::unique_ptr<MediaDevicesDispatcherHost> host_;
+
   std::unique_ptr<media::AudioManager, media::AudioManagerDeleter>
       audio_manager_;
   content::TestBrowserContext browser_context_;
   MediaDeviceEnumeration physical_devices_;
   url::Origin origin_;
 
   std::vector<MediaDeviceInfoArray> enumerated_devices_;
 };
 
 TEST_F(MediaDevicesDispatcherHostTest, EnumerateAudioInputDevices) {
@@ skipping 52 matching lines @@
                  base::Unretained(this)));
   base::RunLoop().RunUntilIdle();
 
   // Verify that the callback for a valid origin does get called.
   EXPECT_CALL(*this, ValidOriginCallback(testing::_));
   host_->EnumerateDevices(
       true, true, true, url::Origin(GURL("http://localhost")),
       base::Bind(&MediaDevicesDispatcherHostTest::ValidOriginCallback,
                  base::Unretained(this)));
   base::RunLoop().RunUntilIdle();
+#if defined(OS_WIN)
+  // On Windows, the underlying MediaStreamManager uses a separate thread for
+  // video capture which must be flushed to guarantee that the callback bound to
+  // EnumerateDevices above is invoked before the end of this test's body.
+  media_stream_manager_->FlushVideoCaptureThreadForTesting();
+  base::RunLoop().RunUntilIdle();
+#endif
 }
 
 };  // namespace content