Removed handle creation and inlined two field index checks

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 11670)
+++ runtime/vm/object.h	(working copy)
@@ -3108,7 +3108,9 @@
                     const AbstractTypeArguments& type_instantiator,
                     Error* malformed_error) const;
 
-  bool IsValidNativeIndex(int index) const;
+  bool IsValidNativeIndex(int index) const {
+    return ((index >= 0) && (index < clazz()->ptr()->num_native_fields_));
+  }
 
   intptr_t GetNativeField(int index) const {
     return *NativeFieldAddr(index);