Revert 78354 - Revert 78236 - Merge r76205, crbug 54262...

WebCore/history/HistoryItem.h

Index: WebCore/history/HistoryItem.h
===================================================================
--- WebCore/history/HistoryItem.h	(revision 78375)
+++ WebCore/history/HistoryItem.h	(working copy)
@@ -88,6 +88,9 @@
     
     PassRefPtr<HistoryItem> copy() const;
     
+    // Resets the HistoryItem to its initial state, as returned by create().
+    void reset();
+    
     const String& originalURLString() const;
     const String& urlString() const;
     const String& title() const;
@@ -141,7 +144,7 @@
 
     void setDocumentSequenceNumber(long long number) { m_documentSequenceNumber = number; }
     long long documentSequenceNumber() const { return m_documentSequenceNumber; }
-    
+
     void setFormInfoFromRequest(const ResourceRequest&);
     void setFormData(PassRefPtr<FormData>);
     void setFormContentType(const String&);
@@ -251,11 +254,19 @@
 
     OwnPtr<Vector<String> > m_redirectURLs;
 
+    // If two HistoryItems have the same item sequence number, then they are
+    // clones of one another.  Traversing history from one such HistoryItem to
+    // another is a no-op.  HistoryItem clones are created for parent and
+    // sibling frames when only a subframe navigates.
     long long m_itemSequenceNumber;
 
+    // If two HistoryItems have the same document sequence number, then they
+    // refer to the same instance of a document.  Traversing history from one
+    // such HistoryItem to another preserves the document.
+    long long m_documentSequenceNumber;
+
     // Support for HTML5 History
     RefPtr<SerializedScriptValue> m_stateObject;
-    long long m_documentSequenceNumber;
     
     // info used to repost form data
     RefPtr<FormData> m_formData;