Make it possible to inherit from any constructable host object

sky/engine/tonic/dart_wrappable.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sky/engine/config.h"
 #include "sky/engine/tonic/dart_wrappable.h"
 
 #include "sky/engine/tonic/dart_class_library.h"
 #include "sky/engine/tonic/dart_error.h"
 #include "sky/engine/tonic/dart_exception_factory.h"
@@ skipping 23 matching lines @@
       Dart_AllocateWithNativeFields(type, kNumberOfNativeFields, native_fields);
   DCHECK(!LogIfError(wrapper));
 
   info.ref_object(this);  // Balanced in FinalizeDartWrapper.
   dart_wrapper_ = Dart_NewPrologueWeakPersistentHandle(
       wrapper, this, info.size_in_bytes, &FinalizeDartWrapper);
 
   return wrapper;
 }
 
+void DartWrappable::AssociateWithDartWrapper(Dart_NativeArguments args) {
+  DCHECK(!dart_wrapper_);
+
+  Dart_Handle wrapper = Dart_GetNativeArgument(args, 0);
+  CHECK(!LogIfError(wrapper));
+
+  intptr_t native_fields[kNumberOfNativeFields];
+  CHECK(!LogIfError(Dart_GetNativeFieldsOfArgument(
+      args, 0, kNumberOfNativeFields, native_fields)));

[esprehn, 2015/02/20 06:56:10]

So all things have the same number of native fields?

[abarth-chromium, 2015/02/20 07:00:34]

Yes.  Always two there are.

+  CHECK(!native_fields[kPeerIndex]);
+  CHECK(!native_fields[kWrapperInfoIndex]);
+
+  const DartWrapperInfo& info = GetDartWrapperInfo();
+  CHECK(!LogIfError(Dart_SetNativeInstanceField(
+      wrapper, kPeerIndex, reinterpret_cast<intptr_t>(this))));
+  CHECK(!LogIfError(Dart_SetNativeInstanceField(
+      wrapper, kWrapperInfoIndex, reinterpret_cast<intptr_t>(&info))));
+
+  info.ref_object(this);  // Balanced in FinalizeDartWrapper.
+  dart_wrapper_ = Dart_NewPrologueWeakPersistentHandle(
+      wrapper, this, info.size_in_bytes, &FinalizeDartWrapper);
+}
+
 void DartWrappable::FinalizeDartWrapper(void* isolate_callback_data,
                                         Dart_WeakPersistentHandle wrapper,
                                         void* peer) {
   DartWrappable* wrappable = reinterpret_cast<DartWrappable*>(peer);
   wrappable->dart_wrapper_ = nullptr;
   const DartWrapperInfo& info = wrappable->GetDartWrapperInfo();
   info.deref_object(wrappable);  // Balanced in CreateDartWrapper.
 }
 
 DartWrappable* DartConverterWrappable::FromDart(Dart_Handle handle) {
@@ skipping 32 matching lines @@
       args, index, DartWrappable::kNumberOfNativeFields, native_fields);
   if (Dart_IsError(result)) {
     exception = Dart_NewStringFromCString(DartError::kInvalidArgument);
     return nullptr;
   }
   return reinterpret_cast<DartWrappable*>(
       native_fields[DartWrappable::kPeerIndex]);
 }
 
 }  // namespace blink