anchor.diff:  /// The filename is of the form "<main output file>_<name>.part.js".
   /// If [addExtension] is false, the ".part.js" suffix is left out.
   String deferredPartFileName(CompilerOptions options, String name,
  -    {bool addExtension: true}) {
  +    {bool addExtension = true}) {
     assert(name != "");
     String outPath = options.outputUri != null ? options.outputUri.path : "out";
     String outName = outPath.substring(outPath.lastIndexOf('/') + 1);
  
positive.code: 
    /// Returns the [OutputUnit] where [cls]'s type belongs.
    // TODO(joshualitt): see above TODO regarding allowNull.
    OutputUnit outputUnitForClassType(ClassEntity cls, {bool allowNull: false}) {
      if (!isProgramSplit) return mainOutputUnit;
      OutputUnit unit = _classTypeToUnit[cls];
      assert(allowNull || unit != null, 'No output unit for type $cls');
  
negative.code: 
    CommonElements get commonElements => elementMap.commonElements;
  
    void add(ir.Expression node, {bool required = true}) {
      ConstantValue constant = elementMap
          .getConstantValue(staticTypeContext, node, requireConstant: required);
      if (constant != null) {
  