Move Document::m_inStyleRecalc into DocumentLifecycle

Source/core/dom/DocumentLifecycle.h

Index: Source/core/dom/DocumentLifecycle.h
diff --git a/Source/core/dom/DocumentLifecycle.h b/Source/core/dom/DocumentLifecycle.h
index c3f919635e833a43521a5a7e401602671935c4f6..22d66867cb20d40480654ac1506bef184ced68d9 100644
--- a/Source/core/dom/DocumentLifecycle.h
+++ b/Source/core/dom/DocumentLifecycle.h
@@ -41,7 +41,13 @@ 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,
@@ -50,6 +56,7 @@ public:
     DocumentLifecycle();
     ~DocumentLifecycle();
 
+    bool isActive() const { return m_state > Inactive && m_state < Stopping; }
     State state() const { return m_state; }
 
     void advanceTo(State);