Fix data race on Debug::thread_local_.current_debug_scope_

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index 9b14afcb34914b9c0d0c8741c965ab69b1c846be..a95ecf27e847ab12b12ac375c1468d655bbb1d7c 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -8,6 +8,7 @@
 #include "src/allocation.h"
 #include "src/arguments.h"
 #include "src/assembler.h"
+#include "src/base/atomicops.h"
 #include "src/base/platform/platform.h"
 #include "src/execution.h"
 #include "src/factory.h"
@@ -459,7 +460,10 @@ class Debug {
   }
 
   // Flags and states.
-  DebugScope* debugger_entry() { return thread_local_.current_debug_scope_; }
+  DebugScope* debugger_entry() {
+    return reinterpret_cast<DebugScope*>(
+        base::NoBarrier_Load(&thread_local_.current_debug_scope_));
+  }
   inline Handle<Context> debug_context() { return debug_context_; }
   void set_live_edit_enabled(bool v) { live_edit_enabled_ = v; }
   bool live_edit_enabled() const {
@@ -470,7 +474,7 @@ class Debug {
   inline bool is_loaded() const { return !debug_context_.is_null(); }
   inline bool has_break_points() const { return has_break_points_; }
   inline bool in_debug_scope() const {
-    return thread_local_.current_debug_scope_ != NULL;
+    return !!base::NoBarrier_Load(&thread_local_.current_debug_scope_);
   }
   void set_disable_break(bool v) { break_disabled_ = v; }
 
@@ -599,7 +603,7 @@ class Debug {
   class ThreadLocal {
    public:
     // Top debugger entry.
-    DebugScope* current_debug_scope_;
+    base::AtomicWord current_debug_scope_;
 
     // Counter for generating next break id.
     int break_count_;