Add a lifecycle state machine for Page

third_party/WebKit/Source/core/frame/FrameLifecycle.h

Index: third_party/WebKit/Source/core/frame/FrameLifecycle.h
diff --git a/third_party/WebKit/Source/core/frame/FrameLifecycle.h b/third_party/WebKit/Source/core/frame/FrameLifecycle.h
new file mode 100644
index 0000000000000000000000000000000000000000..e75b634295df90e45f5c615116c87f5f6e63ce3d
--- /dev/null
+++ b/third_party/WebKit/Source/core/frame/FrameLifecycle.h
@@ -0,0 +1,33 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FrameLifecycle_h
+#define FrameLifecycle_h
+
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class FrameLifecycle {
+  WTF_MAKE_NONCOPYABLE(FrameLifecycle);
+
+ public:
+  enum State {
+    Attached,
+    Detaching,
+    Detached,
+  };
+
+  FrameLifecycle();
+
+  State state() const { return m_state; }
+  void advanceTo(State);
+
+ private:
+  State m_state;
+};
+
+}  // namespace blink
+
+#endif  // FrameLifecycle_h