Modify backend strategy and how we access the closure converter.

pkg/compiler/lib/src/backend_strategy.dart

Index: pkg/compiler/lib/src/backend_strategy.dart
diff --git a/pkg/compiler/lib/src/backend_strategy.dart b/pkg/compiler/lib/src/backend_strategy.dart
index fe1ebedd7517b5ab46c1ea7e12d914800dc14ade..72f11c702b8820481e3782a87413ac3670b7ca56 100644
--- a/pkg/compiler/lib/src/backend_strategy.dart
+++ b/pkg/compiler/lib/src/backend_strategy.dart
@@ -4,6 +4,8 @@
 
 library dart2js.backend_strategy;
 
+import 'closure.dart' show ClosureConversionTask;
+import 'compiler.dart' show Compiler;
 import 'enqueue.dart';
 import 'io/source_information.dart';
 import 'js_backend/js_backend.dart';
@@ -19,8 +21,9 @@ abstract class BackendStrategy {
   /// Create the [ClosedWorldRefiner] for [closedWorld].
   ClosedWorldRefiner createClosedWorldRefiner(ClosedWorld closedWorld);
 
-  /// Create closure classes for local functions.
-  void convertClosures(ClosedWorldRefiner closedWorldRefiner);
+  /// Create the task that analyzes the code to see what closures need to be
+  /// rewritten.
+  ClosureConversionTask createClosureConversionTask(Compiler compiler);
 
   /// The [Sorter] used for sorting elements in the generated code.
   Sorter get sorter;