Extract ClosedWorldImpl from WorldImpl.

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

Index: pkg/compiler/lib/src/universe/function_set.dart
diff --git a/pkg/compiler/lib/src/universe/function_set.dart b/pkg/compiler/lib/src/universe/function_set.dart
index 0fb00187f1daab198ecb8b13807d6c59c539d192..e631e507a50a73587f6774b027257c8a2c6fa93c 100644
--- a/pkg/compiler/lib/src/universe/function_set.dart
+++ b/pkg/compiler/lib/src/universe/function_set.dart
@@ -13,13 +13,8 @@ import '../world.dart' show ClosedWorld;
 import 'selector.dart' show Selector;
 import 'world_builder.dart' show ReceiverConstraint;
 
-// TODO(kasperl): This actually holds getters and setters just fine
-// too and stricly they aren't functions. Maybe this needs a better
-// name -- something like ElementSet seems a bit too generic.
-class FunctionSet {
-  final ClosedWorld closedWorld;
+class FunctionSetBuilder {
   final Map<String, FunctionSetNode> nodes = new Map<String, FunctionSetNode>();
-  FunctionSet(this.closedWorld);
 
   FunctionSetNode newNode(String name) => new FunctionSetNode(name);
 
@@ -41,6 +36,20 @@ class FunctionSet {
     }
   }
 
+  FunctionSet close(ClosedWorld closedWorld) {
+    return new FunctionSet(closedWorld, nodes);
+  }
+}
+
+// TODO(kasperl): This actually holds getters and setters just fine
+// too and stricly they aren't functions. Maybe this needs a better
+// name -- something like ElementSet seems a bit too generic.
+class FunctionSet {
+  final ClosedWorld closedWorld;
+  final Map<String, FunctionSetNode> nodes;
+
+  FunctionSet(this.closedWorld, this.nodes);
+
   bool contains(Element element) {
     assert(element.isInstanceMember);
     assert(!element.isAbstract);