Add an unimplemented history API to WebView

public/web/WebFrameClient.h

Index: public/web/WebFrameClient.h
diff --git a/public/web/WebFrameClient.h b/public/web/WebFrameClient.h
index 2ea883eba0c4cb763adcdf1c7030b8f3020f8cca..4b6e27e8a7a954c60f725aba49d667b1c13a88d7 100644
--- a/public/web/WebFrameClient.h
+++ b/public/web/WebFrameClient.h
@@ -34,6 +34,7 @@
 #include "WebDOMMessageEvent.h"
 #include "WebDataSource.h"
 #include "WebFrame.h"
+#include "WebHistoryItem.h"
 #include "WebIconURL.h"
 #include "WebNavigationPolicy.h"
 #include "WebNavigationType.h"
@@ -164,6 +165,10 @@ public:
         WebLocalFrame*, WebDataSource::ExtraData*, const WebURLRequest&, WebNavigationType,
         WebNavigationPolicy defaultPolicy, bool isRedirect) { return defaultPolicy; }
 
+    // During a history navigation, we may choose to load new subframes from history as well.
+    // This returns such a history item if appropriate.
+    virtual WebHistoryItem historyItemForNewChildFrame(WebFrame*) { return WebHistoryItem(); }
+
 
     // Navigational notifications ------------------------------------------