Add a lifecycle state machine for Document

Source/core/dom/DocumentLifecycle.h

Index: Source/core/dom/DocumentLifecycle.h
diff --git a/Source/core/rendering/LayoutIndicator.h b/Source/core/dom/DocumentLifecycle.h
similarity index 79%
copy from Source/core/rendering/LayoutIndicator.h
copy to Source/core/dom/DocumentLifecycle.h
index 6337da949cffa77681e9e88cfbae87eab70d0208..c3f919635e833a43521a5a7e401602671935c4f6 100644
--- a/Source/core/rendering/LayoutIndicator.h
+++ b/Source/core/dom/DocumentLifecycle.h
@@ -28,36 +28,36 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef LayoutIndicator_h
-#define LayoutIndicator_h
+#ifndef DocumentLifecycle_h
+#define DocumentLifecycle_h
 
-#include "wtf/Assertions.h"
+#include "wtf/Noncopyable.h"
 
 namespace WebCore {
 
-#ifndef NDEBUG
-
-class LayoutIndicator {
+class DocumentLifecycle {
+    WTF_MAKE_NONCOPYABLE(DocumentLifecycle);
 public:
-    LayoutIndicator() { ++s_inLayout; }
-    ~LayoutIndicator() { --s_inLayout; }
+    enum State {
+        Uninitialized,
+        Inactive,
+        Active,
+        Stopping,
+        Stopped,
+        Disposed,
+    };
 
-    static bool inLayout() { return s_inLayout; }
+    DocumentLifecycle();
+    ~DocumentLifecycle();
 
-private:
-    static size_t s_inLayout;
-};
+    State state() const { return m_state; }
 
-#else
+    void advanceTo(State);
 
-class LayoutIndicator {
-public:
-    LayoutIndicator() { }
-    ~LayoutIndicator() { }
+private:
+    State m_state;
 };
 
-#endif
-
 }
 
-#endif // LayoutIndicator_h
+#endif