Report hint on unmatched show and hide combinators.

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 'cps_ir_nodes.dart' as cps_ir;
 import '../tracer.dart';
 
 /**
  * If true, show LetCont expressions in output.
  */
 const bool IR_TRACE_LET_CONT = false;
 
 class IRTracer extends TracerUtil implements cps_ir.Visitor {
   EventSink<String> output;
 
@@ skipping 93 matching lines @@
   }
 
   visitLetCont(cps_ir.LetCont node) {
     if (IR_TRACE_LET_CONT) {
       String dummy = names.name(node);
 
       String nameContinuation(cps_ir.Continuation cont) {
         String name = names.name(cont);
         return cont.isRecursive ? '$name*' : name;
       }
-      
+
       String ids = node.continuations.map(nameContinuation).join(', ');
       printStmt(dummy, "LetCont $ids");
     }
     visit(node.body);
   }
 
   visitLetHandler(cps_ir.LetHandler node) {
     if (IR_TRACE_LET_CONT) {
       String dummy = names.name(node);
       String id = names.name(node.handler);
@@ skipping 542 matching lines @@
 
   @override
   visitAwait(cps_ir.Await node) {
     unexpectedNode(node);
   }
 
   visitRefinement(cps_ir.Refinement node) {
     unexpectedNode(node);
   }
 }