Introduce JsStrategy skeleton

pkg/compiler/lib/src/universe/resolution_world_builder.dart

Index: pkg/compiler/lib/src/universe/resolution_world_builder.dart
diff --git a/pkg/compiler/lib/src/universe/resolution_world_builder.dart b/pkg/compiler/lib/src/universe/resolution_world_builder.dart
index 1fb5ca910b9c3be4b0d7c8eb97ec4d3f331f53a7..83963759939d3c61929a43479410d8ae9c33cd89 100644
--- a/pkg/compiler/lib/src/universe/resolution_world_builder.dart
+++ b/pkg/compiler/lib/src/universe/resolution_world_builder.dart
@@ -952,6 +952,7 @@ abstract class KernelResolutionWorldBuilderBase
   ClosedWorld closeWorld() {
     Map<ClassEntity, Set<ClassEntity>> typesImplementedBySubclasses =
         populateHierarchyNodes();
+    _classHierarchyNodes.keys.toList().forEach(_ensureClassSet);
     _closed = true;
     return _closedWorldCache = new KernelClosedWorld(
         commonElements: _commonElements,
@@ -960,6 +961,7 @@ abstract class KernelResolutionWorldBuilderBase
         backendUsage: _backendUsageBuilder.close(),
         constantSystem: _constantSystem,
         resolutionWorldBuilder: this,
+        implementedClasses: _implementedClasses,
         functionSet: _allFunctions.close(),
         allTypedefs: _allTypedefs,
         mixinUses: _mixinUses,