Separate out the concepts of "history entries separated by just a scroll" and

"history entries with the same postdata".  The latter is implied by the former,
but not conversely.  Bug 264964, r=biesi, sr=darin

docshell/shistory/public/nsISHEntry.idl

@@ -49,7 +49,7 @@
 interface nsILayoutHistoryState;
 interface nsIDOMDocument;
 
-[scriptable, uuid(65281BA1-988A-11d3-BDC7-0050040A9B44)]
+[scriptable, uuid(6b596e1f-a3bd-40f9-a7ee-ab3edc7f9960)]
 interface nsISHEntry : nsISupports 
 {
 
@@ -86,6 +86,16 @@ attribute  unsigned long loadType;
  */
 attribute unsigned long ID;
 
+/**
+ * pageIdentifier is an integer that should be the same for two entries
+ * attached to the same docshell only if the two entries are entries for the
+ * same page in the sense that one could go from the state represented by one
+ * to the state represented by the other simply by scrolling (so the entries
+ * are separated by an anchor traversal or a subframe navigation in some other
+ * frame).
+ */
+attribute unsigned long pageIdentifier;
+
 /** attribute to set and get the cache key for the entry */
 attribute nsISupports cacheKey;
 

docshell/shistory/src/nsSHEntry.cpp

@@ -52,6 +52,7 @@ static PRUint32 gEntryID = 0;
 nsSHEntry::nsSHEntry() 
   : mLoadType(0)
   , mID(gEntryID++)
+  , mPageIdentifier(mID)
   , mScrollPositionX(0)
   , mScrollPositionY(0)
   , mIsFrameNavigation(PR_FALSE)
@@ -70,6 +71,7 @@ nsSHEntry::nsSHEntry(const nsSHEntry &other)
   , mLayoutHistoryState(other.mLayoutHistoryState)
   , mLoadType(0)         // XXX why not copy?
   , mID(other.mID)
+  , mPageIdentifier(other.mPageIdentifier)
   , mScrollPositionX(0)  // XXX why not copy?
   , mScrollPositionY(0)  // XXX why not copy?
   , mIsFrameNavigation(other.mIsFrameNavigation)
@@ -215,6 +217,18 @@ NS_IMETHODIMP nsSHEntry::SetID(PRUint32  aID)
   return NS_OK;
 }
 
+NS_IMETHODIMP nsSHEntry::GetPageIdentifier(PRUint32 * aResult)
+{
+  *aResult = mPageIdentifier;
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsSHEntry::SetPageIdentifier(PRUint32 aPageIdentifier)
+{
+  mPageIdentifier = aPageIdentifier;
+  return NS_OK;
+}
+
 NS_IMETHODIMP nsSHEntry::GetIsSubFrame(PRBool * aFlag)
 {
   *aFlag = mIsFrameNavigation;

docshell/shistory/src/nsSHEntry.h

@@ -80,6 +80,7 @@ private:
   nsCOMArray<nsISHEntry>          mChildren;
   PRUint32                        mLoadType;  
   PRUint32                        mID;
+  PRUint32                        mPageIdentifier;
   PRInt32                         mScrollPositionX;
   PRInt32                         mScrollPositionY;
   PRPackedBool                    mIsFrameNavigation;