Preserve the original semantics in the poi tests.

site/try/poi/poi.dart

Index: site/try/poi/poi.dart
diff --git a/site/try/poi/poi.dart b/site/try/poi/poi.dart
index f40705a9f77a8f2f1e259c90d9cbb0ef5c602f77..cb04b8dcfca9b3495fae4f1209fc16b2ddfc31f2 100644
--- a/site/try/poi/poi.dart
+++ b/site/try/poi/poi.dart
@@ -455,7 +455,7 @@ Future<Element> runPoiInternal(
     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);
   }
@@ -565,7 +565,8 @@ class ScriptOnlyFilter implements QueueFilter {
 }
 
 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';
 }