Use the app snapshot when testing with -cdartk.

runtime/vm/kernel_isolate.cc

Index: runtime/vm/kernel_isolate.cc
diff --git a/runtime/vm/kernel_isolate.cc b/runtime/vm/kernel_isolate.cc
index e10391cdb932a78d8b5af423750ebcdb36eb3229..d2b5345e4e49d60a4450222585f5ddfc6d0a9d24 100644
--- a/runtime/vm/kernel_isolate.cc
+++ b/runtime/vm/kernel_isolate.cc
@@ -70,6 +70,10 @@ class RunKernelTask : public ThreadPool::Task {
 
     Dart_IsolateFlags api_flags;
     Isolate::FlagsInitialize(&api_flags);
+    // Do not inherit the values from the main isolate. The DFE app snapshot
+    // is created in production mode, so it must run in production mode.
+    api_flags.enable_type_checks = false;
+    api_flags.enable_asserts = false;
 
     isolate = reinterpret_cast<Isolate*>(create_callback(
         KernelIsolate::kName, NULL, NULL, NULL, &api_flags, NULL, &error));