Provide ability to patch external functions in a class that has already been finalized. The follow…

runtime/vm/class_finalizer.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 "vm/class_finalizer.h"
 
 #include "vm/code_generator.h"
 #include "vm/flags.h"
 #include "vm/heap.h"
 #include "vm/isolate.h"
@@ skipping 2409 matching lines @@
   }
   // A top level class is parsed eagerly so just finalize it.
   if (cls.IsTopLevel()) {
     FinalizeClass(cls);
   } else {
     // This class should not contain any functions or user-defined fields yet,
     // because it has not been compiled yet. There may however be metadata
     // fields because type parameters are parsed before the class body. Since
     // 'ResolveAndFinalizeMemberTypes(cls)' has not been called yet, unfinalized
     // member types could choke the snapshotter.
-    ASSERT(Array::Handle(cls.functions()).Length() == 0);
+    // Or
+    // if the class is being refinalized because a patch is being applied
+    // after the class has been finalized then it is ok for the class to have
+    // functions.
+    ASSERT((Array::Handle(cls.functions()).Length() == 0) ||
+           cls.is_refinalize_after_patch());
   }
 }
 
 
 void ClassFinalizer::FinalizeClass(const Class& cls) {
   Thread* thread = Thread::Current();
   HANDLESCOPE(thread);
   ASSERT(cls.is_type_finalized());
   if (cls.is_finalized()) {
     return;
@@ skipping 864 matching lines @@
   ASSERT(fields_array.Length() == ByteBuffer::NumberOfFields());
   field ^= fields_array.At(0);
   ASSERT(field.Offset() == ByteBuffer::data_offset());
   name ^= field.name();
   expected_name ^= String::New("_data");
   ASSERT(String::EqualsIgnoringPrivateKey(name, expected_name));
 #endif
 }
 
 }  // namespace dart