Delay Class parsing until the class is actually used.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
===================================================================
--- runtime/vm/dart_api_impl.cc	(revision 23046)
+++ runtime/vm/dart_api_impl.cc	(working copy)
@@ -3051,6 +3051,10 @@
 
   if (obj.IsClass()) {
     const Class& cls = Class::Cast(obj);
+    const Error& error = Error::Handle(isolate, cls.EnsureIsFinalized(isolate));
+    if (!error.IsNull()) {
+      return Api::NewHandle(isolate, error.raw());
+    }
     const Array& func_array = Array::Handle(cls.functions());
 
     // Some special types like 'dynamic' have a null functions list.
@@ -3391,6 +3395,10 @@
 
   if (obj.IsClass()) {
     const Class& cls = Class::Cast(obj);
+    const Error& error = Error::Handle(isolate, cls.EnsureIsFinalized(isolate));
+    if (!error.IsNull()) {
+      return Api::NewHandle(isolate, error.raw());
+    }
     const Array& field_array = Array::Handle(cls.fields());
 
     // Some special types like 'dynamic' have a null fields list.