Decouple WorkItem from Compiler

tests/compiler/dart2js/resolver_test.dart

Index: tests/compiler/dart2js/resolver_test.dart
diff --git a/tests/compiler/dart2js/resolver_test.dart b/tests/compiler/dart2js/resolver_test.dart
index f88787b710fd9d8cac4444ff0b42e27e62371b60..7be75ef14365b389e3f7e42f19a74afc2e8de38a 100644
--- a/tests/compiler/dart2js/resolver_test.dart
+++ b/tests/compiler/dart2js/resolver_test.dart
@@ -16,6 +16,8 @@ import 'package:compiler/src/resolution/registry.dart';
 import 'package:compiler/src/resolution/resolution_result.dart';
 import 'package:compiler/src/resolution/scope.dart';
 import 'package:compiler/src/resolution/tree_elements.dart';
+import 'package:compiler/src/universe/use.dart';
+import 'package:compiler/src/universe/world_impact.dart';
 
 import 'compiler_helper.dart';
 import 'link_helper.dart';
@@ -241,7 +243,8 @@ Future testSwitch() {
     compiler.resolveStatement("Foo foo;");
     ClassElement fooElement = compiler.mainApp.find("Foo");
     FunctionElement funElement = fooElement.lookupLocalMember("foo");
-    compiler.enqueuer.resolution.addToWorkList(funElement);
+    compiler.enqueuer.resolution.applyImpact(new WorldImpactBuilderImpl()
+      ..registerStaticUse(new StaticUse.foreignUse(funElement)));
     compiler.processQueue(compiler.enqueuer.resolution, null);
     DiagnosticCollector collector = compiler.diagnosticCollector;
     Expect.equals(0, collector.warnings.length);