Define TrackView::Copy, cause all track duplications to invoke it...

... but it does nothing yet.

This will be important to preserve undo/redo behavior of view changes, when
view state is moved out of the proper Track objects.

src/Track.cpp

@@ -43,6 +43,8 @@ and TimeTrack.
 
 #include "TrackPanel.h" // for TrackInfo
 
+#include "tracks/ui/TrackView.h"
+
 #ifdef _MSC_VER
 //Disable truncation warnings
 #pragma warning( disable : 4786 )
@@ -120,7 +122,9 @@ Track::Holder Track::Duplicate() const
    // invoke "virtual constructor" to copy track object proper:
    auto result = Clone();
 
-   // other steps to be added here
+   if (mpView)
+      // Copy view state that might be important to undo/redo
+      TrackView::Get( *result ).Copy( *mpView );
 
    return result;
 }

src/tracks/ui/TrackView.cpp

@@ -24,6 +24,10 @@ TrackView::~TrackView()
 {
 }
 
+void TrackView::Copy( const TrackView & )
+{
+}
+
 TrackView &TrackView::Get( Track &track )
 {
    return *track.GetTrackView();

src/tracks/ui/TrackView.h

@@ -30,6 +30,9 @@ public:
       : CommonTrackCell{ pTrack } {}
    virtual ~TrackView() = 0;
 
+   // Copy view state, for undo/redo purposes
+   virtual void Copy( const TrackView &other );
+
    static TrackView &Get( Track & );
    static const TrackView &Get( const Track & );