ASSERT on renderer lifecycle

Source/core/dom/DocumentLifecycle.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 81 matching lines @@
         State m_to;
     };
 
     DocumentLifecycle();
     ~DocumentLifecycle();
 
     bool isActive() const { return m_state > Inactive && m_state < Stopping; }
     State state() const { return m_state; }
 
     bool stateAllowsTreeMutations() const;
+    bool stateAllowsRenderTreeMutations() const;
 
     void advanceTo(State);
     void ensureStateAtMost(State);
 
 private:
 #if !ASSERT_DISABLED
     bool canAdvanceTo(State) const;
     bool canRewindTo(State) const;
 #endif
 
     State m_state;
 };
 
 inline bool DocumentLifecycle::stateAllowsTreeMutations() const
 {
     // FIXME: We should not allow mutations in InPreLayout or AfterPerformLayout either,
     // but we need to fix MediaList listeners and plugins first.
     return m_state != InStyleRecalc
         && m_state != InPerformLayout
         && m_state != InCompositingUpdate;
 }
 
+inline bool DocumentLifecycle::stateAllowsRenderTreeMutations() const
+{
+    return m_state == InStyleRecalc;
+}
+
 }
 
 #endif