[Mojo Video Capture] Add content_browsertest for exercising video capture

content/browser/renderer_host/media/media_devices_manager_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_manager.h"
 
 #include <memory>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 126 matching lines @@
     run_loop->Quit();
   }
 
  protected:
   void SetUp() override {
     audio_manager_.reset(new MockAudioManager());
     video_capture_manager_ = new VideoCaptureManager(
         std::unique_ptr<media::VideoCaptureDeviceFactory>(
             new MockVideoCaptureDeviceFactory()),
         base::ThreadTaskRunnerHandle::Get());
-    video_capture_manager_->RegisterListener(nullptr);
     video_capture_device_factory_ = static_cast<MockVideoCaptureDeviceFactory*>(
         video_capture_manager_->video_capture_device_factory());
     media_devices_manager_.reset(new MediaDevicesManager(
         audio_manager_.get(), video_capture_manager_, nullptr));
   }
 
   void EnableCache(MediaDeviceType type) {
     media_devices_manager_->SetCachePolicy(
         type, MediaDevicesManager::CachePolicy::SYSTEM_MONITOR);
   }
@@ skipping 409 matching lines @@
   media_devices_manager_->OnDevicesChanged(base::SystemMonitor::DEVTYPE_AUDIO);
   media_devices_manager_->OnDevicesChanged(
       base::SystemMonitor::DEVTYPE_VIDEO_CAPTURE);
   base::RunLoop().RunUntilIdle();
   EXPECT_EQ(num_audio_input_devices, notification_all_audio_input.size());
   EXPECT_EQ(num_video_input_devices, notification_all_video_input.size());
   EXPECT_EQ(num_audio_output_devices, notification_all_audio_output.size());
 }
 
 }  // namespace content