dart2js: Fix checked mode test failures due to type annotation.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
index 5bf72b350e24a1fa90501dd5dc136846bde86f77..550cc634c2e4bc5634da80fc64a9c44652c52f2a 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
@@ -1231,7 +1231,7 @@ class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
     // Preprocess: compute a list of cases that are the target of continue.
     // These are the so-called 'recursive' cases.
     List<JumpTarget> continueTargets = <JumpTarget>[];
-    List<ast.SwitchCase> switchCases = node.cases.nodes.toList();
+    List<ast.Node> switchCases = node.cases.nodes.toList();
     for (ast.SwitchCase switchCase in switchCases) {
       for (ast.Node labelOrCase in switchCase.labelsAndCases) {
         if (labelOrCase is ast.Label) {