Proof of concept implementation of context based history filtering.

content/public/browser/web_contents_observer.h

Index: content/public/browser/web_contents_observer.h
diff --git a/content/public/browser/web_contents_observer.h b/content/public/browser/web_contents_observer.h
index b040d64223fe81a143daaedff660bad609e10dd2..53a17a8a66615ae49232fc15cda7671f6061ddb6 100644
--- a/content/public/browser/web_contents_observer.h
+++ b/content/public/browser/web_contents_observer.h
@@ -274,6 +274,7 @@ class CONTENT_EXPORT WebContentsObserver : public IPC::Listener,
   // title was explicitly set, |explicit_set| is true, otherwise the title was
   // synthesized and |explicit_set| is false.
   virtual void TitleWasSet(NavigationEntry* entry, bool explicit_set) {}
+  virtual void SetHistoryContext(NavigationEntry* entry, int context) {}
 
   virtual void AppCacheAccessed(const GURL& manifest_url,
                                 bool blocked_by_policy) {}