anchor.diff:  #import('../leg.dart');
   
   final bool GENERATE_SSA_TRACE = false;
  +final String SSA_TRACE_FILTER = null;
   
   class HTracer extends HGraphVisitor implements Tracer {
     int indent = 0;
     final RandomAccessFile output;
     final bool enabled = GENERATE_SSA_TRACE;
  +  bool traceActive = false;
   
     HTracer([String path = "dart.cfg"])
         : output = GENERATE_SSA_TRACE ? new File(path).openSync(FileMode.WRITE)
  
positive.code:   }
  
    void traceGraph(String name, HGraph graph) {
      if (!enabled) return;
      tag("cfg", () {
        printProperty("name", name);
        visitDominatorTree(graph);
  
negative.code:   }
  
    void traceCompilation(String methodName) {
      if (!enabled) return;
      traceActive =
          SSA_TRACE_FILTER == null || methodName.contains(SSA_TRACE_FILTER);
      if (!traceActive) return;
      tag("compilation", () {
        printProperty("name", methodName);
        printProperty("method", methodName);
  