[POC-WIP] Link window focus tokens with ExecutionContext.

Source/core/dom/ExecutionContext.h

Index: Source/core/dom/ExecutionContext.h
diff --git a/Source/core/dom/ExecutionContext.h b/Source/core/dom/ExecutionContext.h
index 6decfb99508f6db8a091a40f09768bd144d571bd..26e388315037188b74c1df5d8866b52d847baf16 100644
--- a/Source/core/dom/ExecutionContext.h
+++ b/Source/core/dom/ExecutionContext.h
@@ -133,6 +133,10 @@ public:
     virtual EventTarget* errorEventTarget() = 0;
     virtual EventQueue* eventQueue() const = 0;
 
+    void giveWindowFocusToken();
+    void consumeWindowFocusToken();
+    bool isWindowFocusAllowed() const;
+
 protected:
     ExecutionContext();
     virtual ~ExecutionContext();
@@ -177,6 +181,9 @@ private:
     // ExecutionContext's members (notably m_timeouts) is called before they are destructed,
     // m_lifecycleNotifer should be placed *after* such members.
     OwnPtr<ContextLifecycleNotifier> m_lifecycleNotifier;
+
+    // TODO:
+    int m_windowFocusToken;
 };
 
 } // namespace blink