Make assertion scopes thread safe.

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index de7e35e5919e65e5cd46cb666383411aa753bbf6..5a06baaf9458876a4567a296a19dd809a2e3abcd 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -31,6 +31,7 @@
 #include "../include/v8-debug.h"
 #include "allocation.h"
 #include "apiutils.h"
+#include "assert-scope.h"
 #include "atomicops.h"
 #include "builtins.h"
 #include "contexts.h"
@@ -994,10 +995,6 @@ class Isolate {
   }
 
   int* code_kind_statistics() { return code_kind_statistics_; }
-
-  HandleDereferenceGuard::State HandleDereferenceGuardState();
-
-  void SetHandleDereferenceGuardState(HandleDereferenceGuard::State state);
 #endif
 
 #if defined(V8_TARGET_ARCH_ARM) && !defined(__arm__) || \
@@ -1310,9 +1307,6 @@ class Isolate {
   HistogramInfo heap_histograms_[LAST_TYPE + 1];
   JSObject::SpillInformation js_spill_information_;
   int code_kind_statistics_[Code::NUMBER_OF_KINDS];
-
-  HandleDereferenceGuard::State compiler_thread_handle_deref_state_;
-  HandleDereferenceGuard::State execution_thread_handle_deref_state_;
 #endif
 
 #ifdef ENABLE_DEBUGGER_SUPPORT