Throw illegal argument exception when

vm/snapshot.h

Index: vm/snapshot.h
===================================================================
--- vm/snapshot.h	(revision 14802)
+++ vm/snapshot.h	(working copy)
@@ -482,6 +482,29 @@
   ObjectStore* object_store() const { return object_store_; }
 
  private:
+  class NoGCDuringSnapshotWriteScope : public ValueObject {
+   public:
+#if defined(DEBUG)
+    NoGCDuringSnapshotWriteScope() {
+      Isolate::Current()->IncrementNoGCScopeDepth();
+    }
+    ~NoGCDuringSnapshotWriteScope() {
+      Isolate::Current()->DecrementNoGCScopeDepth();
+    }
+    void Reset() const {
+      Isolate::Current()->ResetNoGCScopeDepth();
+    }
+#else  // defined(DEBUG)
+    NoGCDuringSnapshotWriteScope() {}
+    ~NoGCDuringSnapshotWriteScope() {}
+    void Reset() const {}
+#endif  // defined(DEBUG)
+   private:
+    DISALLOW_COPY_AND_ASSIGN(NoGCDuringSnapshotWriteScope);
+  };
+  void ThrowIllegalArgException(const NoGCDuringSnapshotWriteScope& no_gc,
+                                const char* msg);
+
   Snapshot::Kind kind_;
   ObjectStore* object_store_;  // Object store for common classes.
   ClassTable* class_table_;  // Class table for the class index to class lookup.