Make CompilerTask independent of compiler.

pkg/compiler/lib/src/closure.dart

Index: pkg/compiler/lib/src/closure.dart
diff --git a/pkg/compiler/lib/src/closure.dart b/pkg/compiler/lib/src/closure.dart
index 5d5b1287a8aa534baf7e9281ee672544e3edbb3a..b0f01b8058020f2b92f6e7ec2bbe75c666ff0adf 100644
--- a/pkg/compiler/lib/src/closure.dart
+++ b/pkg/compiler/lib/src/closure.dart
@@ -24,12 +24,16 @@ import 'universe/universe.dart' show Universe;
 
 class ClosureTask extends CompilerTask {
   Map<Node, ClosureClassMap> closureMappingCache;
+  Compiler compiler;
   ClosureTask(Compiler compiler)
       : closureMappingCache = new Map<Node, ClosureClassMap>(),
-        super(compiler);
+        compiler = compiler,
+        super(compiler.measurer);
 
   String get name => "Closure Simplifier";
 
+  DiagnosticReporter get reporter => compiler.reporter;
+
   ClosureClassMap computeClosureToClassMapping(ResolvedAst resolvedAst) {
     return measure(() {
       Element element = resolvedAst.element;