Support "await a stable state" and "provide a stable state"

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index b6c9cfd3474f0602b2c1e1f176e2d751128616cf..4c31679b2f26a9b6d5252bb3f92b35d02f7eab78 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -137,6 +137,7 @@
 #include "core/html/HTMLStyleElement.h"
 #include "core/html/HTMLTitleElement.h"
 #include "core/html/PluginDocument.h"
+#include "core/html/StableState.h"
 #include "core/html/forms/FormController.h"
 #include "core/html/parser/HTMLDocumentParser.h"
 #include "core/html/parser/HTMLParserIdioms.h"
@@ -2510,6 +2511,9 @@ bool Document::dispatchBeforeUnloadEvent(Chrome& chrome, bool& didAllowNavigatio
         return true;
     }
 
+    // http://whatwg.org/html#pause
+    StableState::provide();
+
     String text = beforeUnloadEvent->returnValue();
     if (chrome.runBeforeUnloadConfirmPanel(text, m_frame)) {
         didAllowNavigation = true;