Add IR nodes needed for deferred loading.

pkg/kernel/lib/type_checker.dart

Index: pkg/kernel/lib/type_checker.dart
diff --git a/pkg/kernel/lib/type_checker.dart b/pkg/kernel/lib/type_checker.dart
index 45159b2d953bdb9330a6856470d6e1fadab948bd..c6a89373d2e416b251279de6171918c7582f95e8 100644
--- a/pkg/kernel/lib/type_checker.dart
+++ b/pkg/kernel/lib/type_checker.dart
@@ -680,6 +680,16 @@ class TypeCheckingVisitor
   }
 
   @override
+  DartType visitLoadLibrary(LoadLibrary node) {
+    return environment.futureType(const DynamicType());
+  }
+
+  @override
+  DartType visitCheckLibraryIsLoaded(CheckLibraryIsLoaded node) {
+    return environment.objectType;
+  }
+
+  @override
   visitAssertStatement(AssertStatement node) {
     visitExpression(node.condition);
     if (node.message != null) {