Add operators test to source_mapping_test.

pkg/compiler/lib/src/ssa/ssa_tracer.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library ssa.tracer;
 
 import 'dart:async' show EventSink;
 
 import 'ssa.dart';
 import '../js_backend/js_backend.dart';
@@ skipping 371 matching lines @@
     StringBuffer buffer = new StringBuffer();
     buffer.write("Phi(");
     for (int i = 0; i < phi.inputs.length; i++) {
       if (i > 0) buffer.write(", ");
       buffer.write(temporaryId(phi.inputs[i]));
     }
     buffer.write(")");
     return buffer.toString();
   }
 
+  String visitRef(HRef node) {
+    return 'Ref ${temporaryId(node.value)}';
+  }
+
   String visitReturn(HReturn node) => "Return ${temporaryId(node.inputs[0])}";
 
   String visitShiftLeft(HShiftLeft node) => handleInvokeBinary(node, '<<');
   String visitShiftRight(HShiftRight node) => handleInvokeBinary(node, '>>');
 
   String visitStatic(HStatic node)
       => "Static ${node.element.name}";
 
   String visitLazyStatic(HLazyStatic node)
       => "LazyStatic ${node.element.name}";
@@ skipping 121 matching lines @@
   }
 
   String visitAwait(HAwait node) {
     return "await ${temporaryId(node.inputs[0])}";
   }
 
   String visitYield(HYield node) {
     return "yield${node.hasStar ? "*" : ""} ${temporaryId(node.inputs[0])}";
   }
 }