Add support for content hints to VideoTrack.

webrtc/api/test/fakevideotracksource.h

 /*
  *  Copyright 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_API_TEST_FAKEVIDEOTRACKSOURCE_H_
 #define WEBRTC_API_TEST_FAKEVIDEOTRACKSOURCE_H_
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/api/videotracksource.h"
 #include "webrtc/media/base/fakevideocapturer.h"
 
 namespace webrtc {
 
 class FakeVideoTrackSource : public VideoTrackSource {
  public:
+  static rtc::scoped_refptr<FakeVideoTrackSource> Create(bool is_screencast) {
+    return new rtc::RefCountedObject<FakeVideoTrackSource>(is_screencast);
+  }
+
   static rtc::scoped_refptr<FakeVideoTrackSource> Create() {
-    return new rtc::RefCountedObject<FakeVideoTrackSource>();
+    return Create(false);
   }
 
   cricket::FakeVideoCapturer* fake_video_capturer() {
     return &fake_video_capturer_;
   }
 
+  bool is_screencast() const override { return is_screencast_; }
+
  protected:
-  FakeVideoTrackSource()
-      : VideoTrackSource(&fake_video_capturer_,
-                         false /* remote */) {}
+  explicit FakeVideoTrackSource(bool is_screencast)
+      : VideoTrackSource(&fake_video_capturer_, false /* remote */),
+        is_screencast_(is_screencast) {}
   virtual ~FakeVideoTrackSource() {}
 
  private:
   cricket::FakeVideoCapturer fake_video_capturer_;
+  const bool is_screencast_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_TEST_FAKEVIDEOTRACKSOURCE_H_