Preserve the original semantics in the poi tests.

site/try/poi/poi.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 trydart.poi;
 
 import 'dart:async' show
     Completer,
     Future;
 
@@ skipping 437 matching lines @@
 }
 
 Future<Element> runPoiInternal(
     Compiler newCompiler,
     Stopwatch sw,
     LibraryUpdater updater,
     Uri uri,
     int position) {
   bool isFullCompile = cachedCompiler != newCompiler;
   cachedCompiler = newCompiler;
-  if (poiTask == null) {
+  if (poiTask == null || poiTask.compiler != cachedCompiler) {
     poiTask = new PoiTask(cachedCompiler);
     cachedCompiler.tasks.add(poiTask);
   }
 
   if (!isFullCompile) {
     printFormattedTime(
         'Analyzing changes and updating elements took', sw.elapsedMicroseconds);
   }
   sw.reset();
 
@@ skipping 89 matching lines @@
         printWallClock('Skipped ${work.element}.');
         return;
       }
     }
     f(work);
     printWallClock('Processed ${work.element}.');
   }
 }
 
 class PoiTask extends CompilerTask {
-  PoiTask(Compiler compiler) : super(compiler.measurer);
+  final Compiler compiler;
+  PoiTask(Compiler compiler) : compiler = compiler, super(compiler.measurer);
 
   String get name => 'POI';
 }