Support for labels in non-loop code in new dart backend

pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart

 // Copyright (c) 2014, 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 dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 
 import 'cps_ir_nodes.dart' as cps_ir hide Function;
 import '../tracer.dart';
@@ skipping 196 matching lines @@
     if (target is cps_ir.Continuation && target.isReturnContinuation) {
       return "return"; // Do not generate a name for the return continuation
     } else {
       return names.name(ref.definition);
     }
   }
 
   String formatPrimitive(cps_ir.Primitive p) => visit(p);
 
   visitConstant(cps_ir.Constant node) {
-    return "Constant ${node.expression.value}";
+    return "Constant ${node.expression.value.toStructuredString()}";
   }
 
   visitParameter(cps_ir.Parameter node) {
     return "Parameter ${names.name(node)}";
   }
 
   visitContinuation(cps_ir.Continuation node) {
     return "Continuation ${names.name(node)}";
   }
 
@@ skipping 155 matching lines @@
     }
   }
 
   visitContinuation(cps_ir.Continuation c) {
     var old_node = current_block;
     current_block = getBlock(c);
     visit(c.body);
     current_block = old_node;
   }
 }