Make Dart_IdentityEqual live up to its spec and not leak boxing implementation detail.

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/bigint_operations.h"
@@ skipping 479 matching lines @@
     CHECK_CALLBACK_STATE(isolate);
     // This is a VM internal object. Call the C++ method of printing.
     return Api::NewHandle(isolate, String::New(obj.ToCString()));
   }
 }
 
 
 DART_EXPORT bool Dart_IdentityEquals(Dart_Handle obj1, Dart_Handle obj2) {
   Isolate* isolate = Isolate::Current();
   CHECK_ISOLATE(isolate);
-  NoGCScope ngc;
-  return Api::UnwrapHandle(obj1) == Api::UnwrapHandle(obj2);
+  {
+    NoGCScope ngc;
+    if (Api::UnwrapHandle(obj1) == Api::UnwrapHandle(obj2)) {
+      return true;
+    }
+  }
+  const Object& object1 = Object::Handle(isolate, Api::UnwrapHandle(obj1));
+  const Object& object2 = Object::Handle(isolate, Api::UnwrapHandle(obj2));
+  if (object1.IsInstance() && object2.IsInstance()) {
+    return Instance::Cast(object1).IsIdenticalTo(Instance::Cast(object2));
+  }
+  return false;
 }
 
 
 DART_EXPORT Dart_Handle Dart_HandleFromPersistent(
     Dart_PersistentHandle object) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
   ASSERT(state->IsValidPersistentHandle(object));
@@ skipping 3825 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success();
 }
 
 }  // namespace dart