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

Source/core/dom/ExecutionContext.cpp

Index: Source/core/dom/ExecutionContext.cpp
diff --git a/Source/core/dom/ExecutionContext.cpp b/Source/core/dom/ExecutionContext.cpp
index 23f4accad5d1ef752360d1a3de5642ed6c069d92..b3c60b7a26304807f54c5c00a1dbc128e4f9caa5 100644
--- a/Source/core/dom/ExecutionContext.cpp
+++ b/Source/core/dom/ExecutionContext.cpp
@@ -73,6 +73,7 @@ ExecutionContext::ExecutionContext()
     , m_inDispatchErrorEvent(false)
     , m_activeDOMObjectsAreSuspended(false)
     , m_activeDOMObjectsAreStopped(false)
+    , m_windowFocusToken(0)
 {
 }
 
@@ -267,6 +268,23 @@ void ExecutionContext::enforceSandboxFlags(SandboxFlags mask)
     }
 }
 
+void ExecutionContext::giveWindowFocusToken()
+{
+    ++m_windowFocusToken;
+}
+
+void ExecutionContext::consumeWindowFocusToken()
+{
+    if (m_windowFocusToken == 0)
+        return;
+    --m_windowFocusToken;
+}
+
+bool ExecutionContext::isWindowFocusAllowed() const
+{
+    return m_windowFocusToken > 0;
+}
+
 void ExecutionContext::trace(Visitor* visitor)
 {
 #if ENABLE(OILPAN)