Get tools/test.py --noopt green.

runtime/vm/precompiler.cc

 // Copyright (c) 2015, 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 "vm/precompiler.h"
 
 #include "vm/code_patcher.h"
 #include "vm/compiler.h"
 #include "vm/isolate.h"
 #include "vm/log.h"
@@ skipping 862 matching lines @@
   }
 }
 
 
 void Precompiler::FinalizeAllClasses() {
   Library& lib = Library::Handle(Z);
   Class& cls = Class::Handle(Z);
 
   for (intptr_t i = 0; i < libraries_.Length(); i++) {
     lib ^= libraries_.At(i);
+    if (!lib.Loaded()) {
+      String& uri = String::Handle(Z, lib.url());
+      String& msg = String::Handle(Z, String::NewFormatted(
+          "Library '%s' is not loaded. "
+          "Did you forget to call Dart_FinalizeLoading?", uri.ToCString()));
+      Jump(Error::Handle(Z, ApiError::New(msg)));
+    }
+
     ClassDictionaryIterator it(lib, ClassDictionaryIterator::kIteratePrivate);
     while (it.HasNext()) {
       cls = it.GetNextClass();
       if (cls.IsDynamicClass()) {
         continue;  // class 'dynamic' is in the read-only VM isolate.
       }
       cls.EnsureIsFinalized(T);
     }
   }
   I->set_all_classes_finalized(true);
 }
 
 
 }  // namespace dart