Add layout states to DocumentLifecycle state machine

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 829621cb08d332a2438e69c4eae9ba555e4c7b72..8d4dc012bbcdf840066daf054bdfb074ea5f450b 100644
--- a/Source/core/dom/DocumentLifecycle.h
+++ b/Source/core/dom/DocumentLifecycle.h
@@ -43,9 +43,15 @@ public:
         Inactive,
 
         // When the document is active, it traverses these states.
+
         StyleRecalcPending,
         InStyleRecalc,
-        Clean,
+        StyleClean,
+
+        InPreLayout,
+        InPerformLayout,
+        AfterPerformLayout,
+        LayoutClean,
 
         // Once the document starts shuting down, we cannot return
         // to the style/layout/rendering states.
@@ -54,6 +60,34 @@ public:
         Disposed,
     };
 
+    class Scope {
+        WTF_MAKE_NONCOPYABLE(Scope);
+    public:
+        Scope(DocumentLifecycle&, State finalState);
+        ~Scope();
+
+        void setFinalState(State finalState) { m_finalState = finalState; }
+
+    private:
+        DocumentLifecycle& m_lifecycle;
+        State m_finalState;
+    };
+
+    class DeprecatedTransition {
+        WTF_MAKE_NONCOPYABLE(DeprecatedTransition);
+    public:
+        DeprecatedTransition(State from, State to);
+        ~DeprecatedTransition();
+
+        State from() const { return m_from; }
+        State to() const { return m_to; }
+
+    private:
+        DeprecatedTransition* m_previous;
+        State m_from;
+        State m_to;
+    };
+
     DocumentLifecycle();
     ~DocumentLifecycle();
 
@@ -64,7 +98,9 @@ public:
     void rewindTo(State);
 
 private:
+#if !ASSERT_DISABLED
     bool canAdvanceTo(State) const;
+#endif
 
     State m_state;
 };