Serializer enable/disable flags need thread safety.

src/arm/assembler-arm.h

Index: src/arm/assembler-arm.h
diff --git a/src/arm/assembler-arm.h b/src/arm/assembler-arm.h
index 86cb835dbd9e6bdc36f67965f426a8adbb40ddc4..f64cc5c0b3e8993bb08c8d5a5d8bdfcc000a7fe5 100644
--- a/src/arm/assembler-arm.h
+++ b/src/arm/assembler-arm.h
@@ -58,6 +58,11 @@ class CpuFeatures : public AllStatic {
   // is enabled (snapshots must be portable).
   static void Probe();
 
+  // A special case for printing target and features, which we want to do
+  // before initializing the isolate
+  static void SetHintCreatingSnapshot();
+  static void ProbeWithoutIsolate();
+
   // Display target use when compiling.
   static void PrintTarget();
 
@@ -94,6 +99,9 @@ class CpuFeatures : public AllStatic {
   }
 
  private:
+  static void Probe(bool serializer_enabled);
+  static bool hint_creating_snapshot_;
+
   static bool Check(CpuFeature f, unsigned set) {
     return (set & flag2set(f)) != 0;
   }