[WebRTC] Add ScreenCapturerDifferWrapper to share Differ across ScreenCapturers

webrtc/modules/desktop_capture/fake_screen_capturer.cc

Index: webrtc/modules/desktop_capture/fake_screen_capturer.cc
diff --git a/webrtc/modules/desktop_capture/fake_screen_capturer.cc b/webrtc/modules/desktop_capture/fake_screen_capturer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..192992fcff7bd189265018d0a0c8ee4c03494585
--- /dev/null
+++ b/webrtc/modules/desktop_capture/fake_screen_capturer.cc
@@ -0,0 +1,34 @@
+/*
+ *  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.
+ */
+
+#include "webrtc/modules/desktop_capture/fake_screen_capturer.h"
+
+#include <stdint.h>
+
+#include <utility>
+
+namespace webrtc {
+
+FakeScreenCapturer::FakeScreenCapturer()
+    : FakeDesktopCapturer(),
+      // A random number for the fake screen.
+      id_(1378277498) {}
+FakeScreenCapturer::~FakeScreenCapturer() {}
+
+bool FakeScreenCapturer::GetScreenList(ScreenList* list) {
+  list->push_back(Screen{id_});
+  return true;
+}
+
+bool FakeScreenCapturer::SelectScreen(ScreenId id) {
+  return id == kFullDesktopScreenId || id == id_;
+}
+
+}  // namespace webrtc