Add asserts that isolates have a root library set up before they become runnable.

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "vm/class_finalizer.h"
@@ skipping 1483 matching lines @@
 }
 
 
 DART_EXPORT bool Dart_IsolateMakeRunnable(Dart_Isolate isolate) {
   CHECK_NO_ISOLATE(Isolate::Current());
   if (isolate == NULL) {
     FATAL1("%s expects argument 'isolate' to be non-null.",  CURRENT_FUNC);
   }
   // TODO(16615): Validate isolate parameter.
   Isolate* iso = reinterpret_cast<Isolate*>(isolate);
+  if (iso->object_store()->root_library() == Library::null()) {
+    // The embedder should have called Dart_LoadScript by now.
+    return false;
+  }
   return iso->MakeRunnable();
 }
 
 
 // --- Messages and Ports ---
 
 DART_EXPORT void Dart_SetMessageNotifyCallback(
     Dart_MessageNotifyCallback message_notify_callback) {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
@@ skipping 4040 matching lines @@
 
 
 DART_EXPORT void Dart_RegisterRootServiceRequestCallback(
     const char* name,
     Dart_ServiceRequestCallback callback,
     void* user_data) {
   Service::RegisterRootEmbedderCallback(name, callback, user_data);
 }
 
 }  // namespace dart