Introduce OpenWorld.

tests/compiler/dart2js/patch_test.dart

Index: tests/compiler/dart2js/patch_test.dart
diff --git a/tests/compiler/dart2js/patch_test.dart b/tests/compiler/dart2js/patch_test.dart
index cd74639d47b5a67ae83c6ab8e894878e6b7f3acc..89b98964e3c6d4ca540c1d26651d53e7812d9872 100644
--- a/tests/compiler/dart2js/patch_test.dart
+++ b/tests/compiler/dart2js/patch_test.dart
@@ -944,8 +944,7 @@ Future testPatchAndSelector() async {
       }
       """,
       runCompiler: true, analyzeOnly: true);
-  World world = compiler.openWorld;
-  world.populate();
+  ClosedWorld world = compiler.openWorld.populate();
 
   ClassElement cls = ensure(compiler, "A",
       compiler.commonElements.coreLibrary.find, expectIsPatched: true);
@@ -966,7 +965,7 @@ Future testPatchAndSelector() async {
   TypeMask typeMask = new TypeMask.exact(cls, world);
   FunctionElement method = cls.implementation.lookupLocalMember('method');
   method.computeType(compiler.resolution);
-  Expect.isTrue(selector.applies(method, world));
+  Expect.isTrue(selector.applies(method, world.backend));
   Expect.isTrue(typeMask.canHit(method, selector, world));
 
   // Check that the declaration method in the declaration class is a target
@@ -976,7 +975,7 @@ Future testPatchAndSelector() async {
   typeMask = new TypeMask.exact(cls, world);
   method = cls.lookupLocalMember('clear');
   method.computeType(compiler.resolution);
-  Expect.isTrue(selector.applies(method, world));
+  Expect.isTrue(selector.applies(method, world.backend));
   Expect.isTrue(typeMask.canHit(method, selector, world));
 
   // Check that the declaration method in the declaration class is a target
@@ -984,7 +983,7 @@ Future testPatchAndSelector() async {
   cls = ensure(compiler, "B", compiler.commonElements.coreLibrary.find);
   cls.ensureResolved(compiler.resolution);
   typeMask = new TypeMask.exact(cls, world);
-  Expect.isTrue(selector.applies(method, world));
+  Expect.isTrue(selector.applies(method, world.backend));
   Expect.isTrue(typeMask.canHit(method, selector, world));
 }