Move Document::m_inStyleRecalc into DocumentLifecycle

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 23 matching lines @@
 #include "wtf/Noncopyable.h"
 
 namespace WebCore {
 
 class DocumentLifecycle {
     WTF_MAKE_NONCOPYABLE(DocumentLifecycle);
 public:
     enum State {
         Uninitialized,
         Inactive,
-        Active,
+
+        // When the document is active, it traverses these states.
+        Clean,
+        InStyleRecalc,
+
+        // Once the document starts shuting down, we cannot return
+        // to the style/layout/rendering states.
         Stopping,
         Stopped,
         Disposed,
     };
 
     DocumentLifecycle();
     ~DocumentLifecycle();
 
+    bool isActive() const { return m_state > Inactive && m_state < Stopping; }
     State state() const { return m_state; }
 
     void advanceTo(State);
 
 private:
     State m_state;
 };
 
 }
 
 #endif