Added following dart API changes to enable more efficient access based

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 25979)
+++ runtime/vm/object.h	(working copy)
@@ -35,6 +35,7 @@
 class FinalizablePersistentHandle;
 class LocalScope;
 class ReusableHandleScope;
+class ReusableObjectHandleScope;
 class Symbols;
 
 #if defined(DEBUG)
@@ -621,6 +622,7 @@
   friend class ExternalTwoByteString;
   friend class Isolate;
   friend class ReusableHandleScope;
+  friend class ReusableObjectHandleScope;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Object);