Avoid handle dereference during graph optimization.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index d43c451e97c0e1645397b7005511b889a613fdbd..286f674561041f9acfe15a2ad1c0f97ae184c9c0 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -969,6 +969,9 @@ class Isolate {
   }
 
   int* code_kind_statistics() { return code_kind_statistics_; }
+
+  bool allow_handle_deref() { return allow_handle_deref_; }
+  void set_allow_handle_deref(bool allow) { allow_handle_deref_ = allow; }
 #endif
 
 #if defined(V8_TARGET_ARCH_ARM) && !defined(__arm__) || \
@@ -1266,6 +1269,8 @@ class Isolate {
   HistogramInfo heap_histograms_[LAST_TYPE + 1];
   JSObject::SpillInformation js_spill_information_;
   int code_kind_statistics_[Code::NUMBER_OF_KINDS];
+
+  bool allow_handle_deref_;
 #endif
 
 #ifdef ENABLE_DEBUGGER_SUPPORT