[DesktopCapturer] FallbackDesktopCapturerWrapper and its tests

webrtc/modules/desktop_capture/fallback_desktop_capturer_wrapper.h

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_DESKTOP_CAPTURE_FALLBACK_DESKTOP_CAPTURER_WRAPPER_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_FALLBACK_DESKTOP_CAPTURER_WRAPPER_H_
+
+#include <memory>
+
+#include "webrtc/modules/desktop_capture/desktop_capturer.h"
+#include "webrtc/modules/desktop_capture/desktop_capture_types.h"
+#include "webrtc/modules/desktop_capture/desktop_frame.h"
+#include "webrtc/modules/desktop_capture/shared_memory.h"
+
+namespace webrtc {
+
+// A DesktopCapturer wrapper owns two DesktopCapturer implementations. If the
+// main DesktopCapturer fails, it uses the secondary one instead. Two capturers
+// are expected to return same SourceList, and the meaning of each SourceId is
+// identical, otherwise FallbackDesktopCapturerWrapper may return frames from
+// different sources. Using asynchronized DesktopCapturer implementations with
+// SharedMemoryFactory is not supported, and may result crash or assertion
+// failure.
+class FallbackDesktopCapturerWrapper final : public DesktopCapturer,
+                                             public DesktopCapturer::Callback {
+ public:
+  FallbackDesktopCapturerWrapper(
+      std::unique_ptr<DesktopCapturer> main_capturer,
+      std::unique_ptr<DesktopCapturer> secondary_capturer);
+  ~FallbackDesktopCapturerWrapper() override;
+
+  // DesktopCapturer interface.
+  void Start(DesktopCapturer::Callback* callback) override;
+  void SetSharedMemoryFactory(
+      std::unique_ptr<SharedMemoryFactory> shared_memory_factory) override;
+  void CaptureFrame() override;
+  void SetExcludedWindow(WindowId window) override;
+  bool GetSourceList(SourceList* sources) override;
+  bool SelectSource(SourceId id) override;
+  bool FocusOnSelectedSource() override;
+
+ private:
+  // DesktopCapturer::Callback interface.
+  void OnCaptureResult(Result result,
+                       std::unique_ptr<DesktopFrame> frame) override;
+
+  const std::unique_ptr<DesktopCapturer> main_capturer_;
+  const std::unique_ptr<DesktopCapturer> secondary_capturer_;
+  std::unique_ptr<SharedMemoryFactory> shared_memory_factory_;
+  bool main_capturer_permanent_error_ = false;
+  DesktopCapturer::Callback* callback_ = nullptr;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_FALLBACK_DESKTOP_CAPTURER_WRAPPER_H_