anchor.diff:  part of index_geometry;
   
  +/// List of integers used to describe how the vertices in a [VertexArray] are
  +/// connected into geometry primitives.
   class IndexList extends DelegatingList<int> implements Uint16List {
     final Uint16List delegate;
   
  
positive.code: 
    IndexList._fromUint16List(this.delegate, this.isDynamic);
  
    IndexList.fromList(List<int> elements)
        : isDynamic = false,
          delegate = new Uint16List.fromList(elements);
  
    IndexList.dynamicFromList(List<int> elements)
        : isDynamic = true,
          delegate = new Uint16List.fromList(elements);
  
    IndexList.view(ByteBuffer buffer, [int offsetInBytes = 0, int length])
        : isDynamic = false,
          delegate = new Uint16List.view(buffer, offsetInBytes, length);
  
    IndexList.dynamicView(ByteBuffer buffer, [int offsetInBytes = 0, int length])
        : isDynamic = true,
          delegate = new Uint16List.view(buffer, offsetInBytes, length);
  
negative.code:   /// dynamic can still be modified.
    final bool isDynamic;
  
    static const int BYTES_PER_ELEMENT = Uint16List.BYTES_PER_ELEMENT;
  
    /// Instantiates a new [IndexList] of the given [length] with default indices.
    ///
    /// The default indices start at `0` and increment by `1` up till
    /// `length - 1`: `0`, `1`, `2`, ..., `length - 1`.
    factory IndexList(int length) => new IndexList._internal(length, false);
  
    /// Instantiates a new [IndexList] of the given [length] with default indices,
    /// marked as dynamic.
    ///
    /// The default indices start at `0` and increment by `1` up till
    /// `length - 1`: `0`, `1`, `2`, ..., `length - 1`.
    ///
    /// When index geometry is marked as dynamic it signals to the rendering
    /// back-end that the indices are intended to be modified regularly, allowing
    /// the rendering back-end to optimize for this. Note that this is merely a
    /// hint that can be used for tuning the performance of a rendering back-end:
    /// the index data for geometry that is not marked as dynamic can still be
    /// modified.
    factory IndexList.dynamic(int length) =>
        new IndexList._internal(length, true);
  
  