[Mojo Video Capture] Introduce abstraction VideoCaptureSystem

media/capture/video/video_capture_system.h

+// Copyright 2017 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.
+
+#ifndef MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_SYSTEM_H_
+#define MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_SYSTEM_H_
+
+#include "media/capture/video/video_capture_device_factory.h"
+#include "media/capture/video/video_capture_device_info.h"
+
+namespace media {
+
+// Layer on top of VideoCaptureDeviceFactory that translates device descriptors
+// to string identifiers and consolidates and caches device descriptors and
+// supported formats into VideoCaptureDeviceInfos.
+class CAPTURE_EXPORT VideoCaptureSystem {
+ public:
+  using DeviceInfoCallback =
+      base::Callback<void(const std::vector<VideoCaptureDeviceInfo>&)>;
+
+  explicit VideoCaptureSystem(
+      std::unique_ptr<VideoCaptureDeviceFactory> factory);
+  ~VideoCaptureSystem();
+
+  // The passed-in |result_callback| must have ownership of the called
+  // VideoCaptureSystem instance to guarantee that it stays alive during the
+  // asynchronous operation.
+  void GetDeviceInfosAsync(const DeviceInfoCallback& result_callback);
+
+  // Creates a VideoCaptureDevice object. Returns nullptr if something goes
+  // wrong.
+  std::unique_ptr<VideoCaptureDevice> CreateDevice(
+      const std::string& device_id);
+
+  media::VideoCaptureDeviceFactory* video_capture_device_factory() const {
+    return factory_.get();
+  }
+
+ private:
+  void OnDescriptorsReceived(
+      const DeviceInfoCallback& result_callback,
+      std::unique_ptr<VideoCaptureDeviceDescriptors> descriptors);
+
+  // Returns nullptr if no descriptor found.
+  const VideoCaptureDeviceInfo* LookupDeviceInfoFromId(
+      const std::string& device_id);
+
+  const std::unique_ptr<VideoCaptureDeviceFactory> factory_;
+  std::vector<VideoCaptureDeviceInfo> devices_info_cache_;
+
+  base::ThreadChecker thread_checker_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_FACTORY_H_