Make v8::Isolate::SetRAILMode thread safe and remove the

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index 0075a4197acaedae9da5f48df0b0fac75caa1cc8..4bc865bfe14e2d57661d9020d6710100808751d7 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1839,7 +1839,7 @@ Isolate::Isolate(bool enable_serializer)
       // TODO(bmeurer) Initialized lazily because it depends on flags; can
       // be fixed once the default isolate cleanup is done.
       random_number_generator_(NULL),
-      rail_mode_(PERFORMANCE_DEFAULT),
+      rail_mode_(PERFORMANCE_ANIMATION),
       serializer_enabled_(enable_serializer),
       has_fatal_error_(false),
       initialized_from_snapshot_(false),
@@ -2995,9 +2995,9 @@ void Isolate::CheckDetachedContextsAfterGC() {
 }
 
 void Isolate::SetRAILMode(RAILMode rail_mode) {
-  rail_mode_ = rail_mode;
+  rail_mode_.SetValue(rail_mode);
   if (FLAG_trace_rail) {
-    PrintIsolate(this, "RAIL mode: %s\n", RAILModeName(rail_mode_));
+    PrintIsolate(this, "RAIL mode: %s\n", RAILModeName(rail_mode));
   }
 }