[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/fake_desktop_capturer.h

Index: webrtc/modules/desktop_capture/fake_desktop_capturer.h
diff --git a/webrtc/modules/desktop_capture/fake_desktop_capturer.h b/webrtc/modules/desktop_capture/fake_desktop_capturer.h
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+/*
+ *  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_FAKE_DESKTOP_CAPTURER_H_
+#define WEBRTC_MODULES_DESKTOP_CAPTURE_FAKE_DESKTOP_CAPTURER_H_
+
+#include <memory>
+#include <utility>
+
+#include "webrtc/modules/desktop_capture/desktop_capturer.h"
+#include "webrtc/modules/desktop_capture/desktop_frame_generator.h"
+#include "webrtc/modules/desktop_capture/shared_desktop_frame.h"
+#include "webrtc/modules/desktop_capture/shared_memory.h"
+
+namespace webrtc {
+
+// A fake implementation of DesktopCapturer or its derived interfaces to
+// generate DesktopFrame for testing purpose.
+//
+// Consumers can provide a FrameGenerator instance to generate instances of
+// DesktopFrame to return for each Capture() function call.
+// If no FrameGenerator provided, FakeDesktopCapturer will always return a
+// nullptr DesktopFrame.
+//
+// Double buffering is guaranteed by the FrameGenerator. FrameGenerator
+// implements in desktop_frame_generator.h guarantee double buffering, they
+// creates a new instance of DesktopFrame each time.
+//
+// T must be DesktopCapturer or its derived interfaces.
+//
+// TODO(zijiehe): Remove template T once we merge ScreenCapturer and
+// WindowCapturer.
+template <typename T>
+class FakeDesktopCapturer : public T {
+ public:
+  FakeDesktopCapturer()
+      : callback_(nullptr),
+        result_(DesktopCapturer::Result::SUCCESS),
+        generator_(nullptr) {}
+
+  ~FakeDesktopCapturer() override {}
+
+  // Decides the result which will be returned in next Capture() callback.
+  void set_result(DesktopCapturer::Result result) { result_ = result; }
+
+  // Uses the |generator| provided as DesktopFrameGenerator, FakeDesktopCapturer
+  // does
+  // not take the ownership of |generator|.
+  void set_frame_generator(DesktopFrameGenerator* generator) {
+    generator_ = generator;
+  }
+
+  // DesktopCapturer interface
+  void Start(DesktopCapturer::Callback* callback) override {
+    callback_ = callback;
+  }
+
+  void Capture(const DesktopRegion& region) override {
+    if (generator_) {
+      std::unique_ptr<DesktopFrame> frame(
+          generator_->GetNextFrame(shared_memory_factory_.get()));
+      if (frame) {
+        callback_->OnCaptureResult(result_, std::move(frame));
+      } else {
+        callback_->OnCaptureResult(DesktopCapturer::Result::ERROR_TEMPORARY,
+                                   nullptr);
+      }
+      return;
+    }
+    callback_->OnCaptureResult(DesktopCapturer::Result::ERROR_PERMANENT,
+                               nullptr);
+  }
+
+  void SetSharedMemoryFactory(
+      std::unique_ptr<SharedMemoryFactory> shared_memory_factory) override {
+    shared_memory_factory_ = std::move(shared_memory_factory);
+  }
+
+ private:
+  DesktopCapturer::Callback* callback_;
+  std::unique_ptr<SharedMemoryFactory> shared_memory_factory_;
+  DesktopCapturer::Result result_;
+  DesktopFrameGenerator* generator_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_DESKTOP_CAPTURE_FAKE_DESKTOP_CAPTURER_H_