Create type masks lazily.

sdk/lib/_internal/compiler/implementation/types/container_tracer.dart

Index: sdk/lib/_internal/compiler/implementation/types/container_tracer.dart
diff --git a/sdk/lib/_internal/compiler/implementation/types/container_tracer.dart b/sdk/lib/_internal/compiler/implementation/types/container_tracer.dart
index 3b663c60cdb1ec5021ed92981d5fcf7bb17f4b41..0abae5dab4ebfece6cdc294af41d5117c9ff870d 100644
--- a/sdk/lib/_internal/compiler/implementation/types/container_tracer.dart
+++ b/sdk/lib/_internal/compiler/implementation/types/container_tracer.dart
@@ -465,6 +465,7 @@ class ContainerTracerVisitor
       LocalsHandler closureLocals = new LocalsHandler<TypeMask>.from(
           locals, node, useOtherTryBlock: false);
       new ContainerTracerVisitor(function, tracer, closureLocals).run();
+      return types.functionType;
     } else {
       // Visiting [analyzedElement].
       FunctionSignature signature = function.computeSignature(compiler);
@@ -475,8 +476,8 @@ class ContainerTracerVisitor
       visit(node.initializers);
       visitingInitializers = false;
       visit(node.body);
+      return null;
     }
-    return types.functionType;
   }
 
   TypeMask visitLiteralList(LiteralList node) {