Implement timestamp translation/filter in VideoCapturer.

webrtc/media/base/videoframefactory.h

Index: webrtc/media/base/videoframefactory.h
diff --git a/webrtc/media/base/videoframefactory.h b/webrtc/media/base/videoframefactory.h
index 985199f646f12d8285547e8eeadefe8b07ed3890..5564ff95ef987d8f550f120b3fe436e3670f74d5 100644
--- a/webrtc/media/base/videoframefactory.h
+++ b/webrtc/media/base/videoframefactory.h
@@ -25,7 +25,7 @@ class VideoFrame;
 // depending on the subclass of VideoFrameFactory.
 class VideoFrameFactory {
  public:
-  VideoFrameFactory() : apply_rotation_(false) {}
+  VideoFrameFactory() : apply_rotation_(false), timestamp_offset_us_(0) {}
   virtual ~VideoFrameFactory() {}
 
   // The returned frame aliases the aliased_frame if the input color
@@ -48,9 +48,15 @@ class VideoFrameFactory {
                                          int output_height) const;
 
   void SetApplyRotation(bool enable) { apply_rotation_ = enable; }
+  // TODO(nisse): Delete this method? Not much use in extending this
+  // class, which we'de like to delete.
+  void SetTimestampOffset(int64_t offset) { timestamp_offset_us_ = offset; }
 
  protected:
   bool apply_rotation_;
+  // Offset added to the capture timestamp, to translate it to the
+  // system monotonic time attached to the produced VideoFrame.
+  int64_t timestamp_offset_us_;
 
  private:
   // An internal pool to avoid reallocations. It is mutable because it