Inform the WebFrameClient of BeforeUnload/Unload handlers

public/web/WebFrameClient.h

Index: public/web/WebFrameClient.h
diff --git a/public/web/WebFrameClient.h b/public/web/WebFrameClient.h
index 62641d2a76f6e397b5b148989bc3f621fb8c0ce5..660fe1d5f766cac3c0739e5dd49a76820363b92d 100644
--- a/public/web/WebFrameClient.h
+++ b/public/web/WebFrameClient.h
@@ -611,6 +611,19 @@ public:
     virtual bool enterFullscreen() { return false; }
     virtual bool exitFullscreen() { return false; }
 
+
+    // Sudden termination --------------------------------------------------
+
+    // Called when an element preventing the sudden termination of the frame is
+    // added or removed. |added| is true if an element was added, false if it
+    // was removed. |type| is the type of element (BeforeUnload handler, Unload
+    // handler).
+    enum SuddenTerminationDisablerType {
+        BeforeUnloadHandler,
+        UnloadHandler,
+    };
+    virtual void suddenTerminationDisablerChanged(bool added, SuddenTerminationDisablerType) { }
+
 protected:
     virtual ~WebFrameClient() { }
 };