Add a lifecycle state machine for Document

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 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * 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 DocumentLifecycle {
+    WTF_MAKE_NONCOPYABLE(DocumentLifecycle);
+public:
+    enum State {
+        Uninitialized,
+        Inactive,
+        Active,
+        Stopping,
+        Stopped,
+        Disposed,
+    };
 
-class LayoutIndicator {
-public:
-    LayoutIndicator() { ++s_inLayout; }
-    ~LayoutIndicator() { --s_inLayout; }
+    DocumentLifecycle();
+    ~DocumentLifecycle();
 
-    static bool inLayout() { return s_inLayout; }
+    State state() const { return m_state; }
+
+    void advanceTo(State);
 
 private:
-    static size_t s_inLayout;
+    State m_state;
 };
 
-#else
-
-class LayoutIndicator {
-public:
-    LayoutIndicator() { }
-    ~LayoutIndicator() { }
-};
-
-#endif
-
 }
 
-#endif // LayoutIndicator_h
+#endif