Added following dart API changes to enable more efficient access based

runtime/vm/dart_api_impl.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_DART_API_IMPL_H_
 #define VM_DART_API_IMPL_H_
 
 #include "vm/allocation.h"
 #include "vm/native_arguments.h"
 #include "vm/object.h"
@@ skipping 188 matching lines @@
   }
   static void SetSmiReturnValue(NativeArguments* args, intptr_t retval) {
     args->SetReturnUnsafe(Smi::New(retval));
   }
   static void SetIntegerReturnValue(NativeArguments* args, intptr_t retval) {
     args->SetReturnUnsafe(Integer::New(retval));
   }
   static void SetDoubleReturnValue(NativeArguments* args, double retval) {
     args->SetReturnUnsafe(Double::New(retval));
   }
+  static void SetWeakHandleReturnValue(NativeArguments* args,
+                                       Dart_WeakPersistentHandle retval);
 
  private:
   // Thread local key used by the API. Currently holds the current
   // ApiNativeScope if any.
   static ThreadLocalKey api_native_key_;
   static Dart_Handle true_handle_;
   static Dart_Handle false_handle_;
   static Dart_Handle null_handle_;
 
   friend class ApiNativeScope;
@@ skipping 25 matching lines @@
   if (isolate->no_callback_scope_depth() != 0) {                               \
     return reinterpret_cast<Dart_Handle>(Api::AcquiredError(isolate));         \
   }                                                                            \
 
 #define ASSERT_CALLBACK_STATE(isolate)                                         \
   ASSERT(isolate->no_callback_scope_depth() == 0)
 
 }  // namespace dart.
 
 #endif  // VM_DART_API_IMPL_H_