Do not submit: high level overview patch.

chrome/browser/sync/glue/tab_node_pool.h

Index: chrome/browser/sync/glue/tab_node_pool.h
diff --git a/chrome/browser/sync/glue/tab_node_pool.h b/chrome/browser/sync/glue/tab_node_pool.h
index 8327d061e08551ecf4fb835e39b06b80f1a613f5..299d9ae710f1cddf7607f60c6ff0b65c85e40c1e 100644
--- a/chrome/browser/sync/glue/tab_node_pool.h
+++ b/chrome/browser/sync/glue/tab_node_pool.h
@@ -23,14 +23,14 @@ class TabNodePool {
 
   // Build a sync tag from tab_node_id.
   static std::string TabIdToTag(const std::string machine_tag,
-                                size_t tab_node_id);
+                                int32 tab_node_id);
 
   // Add a previously allocated tab sync node to our pool. Increases the size
   // of tab_syncid_pool_ by one and marks the new tab node as free.
   // Note: this should only be called when we discover tab sync nodes from
   // previous sessions, not for freeing tab nodes we created through
   // GetFreeTabNode (use FreeTabNode below for that).
-  void AddTabNode(int64 sync_id);
+  void AddTabNode(int64 sync_id, int32 tab_node_id);
 
   // Returns the sync_id for the next free tab node. If none are available,
   // creates a new tab node.
@@ -53,16 +53,22 @@ class TabNodePool {
   // the |tab_syncid_pool_| should always be equal to the amount of tab nodes
   // associated with this machine.
   void FreeTabNode(int64 sync_id);
+  int64 GetOldSyncNode(const int64 sync_node_id);
+
+  void PurgeOldSyncNodes(std::vector<int64>& used_sync_ids);
 
   // Clear tab pool.
   void clear() {
     tab_syncid_pool_.clear();
+    old_sync_ids.clear();
     tab_pool_fp_ = -1;
   }
 
   // Return the number of tab nodes this client currently has allocated
   // (including both free and used nodes)
-  size_t capacity() const { return tab_syncid_pool_.size(); }
+  size_t capacity() const {
+    return tab_syncid_pool_.size() + old_sync_ids.size();
+  }
 
   // Return empty status (all tab nodes are in use).
   bool empty() const { return tab_pool_fp_ == -1; }
@@ -77,9 +83,20 @@ class TabNodePool {
   }
 
  private:
+
+  /* The maximum used tab node id, when creating a new sync node we used
+   * max_used_tab_node_id_ + 1 */
+  int32 max_used_tab_node_id_;
+
   // Pool of all available syncid's for tab's we have created.
   std::vector<int64> tab_syncid_pool_;
 
+  // Pool containing unused sync nodes as a result of session restore.
+  std::vector<int64> session_restore_syncid_nodes_pool_;
+
+  // typedef std::pair<int64, int32> sync_node_pair;
+  std::vector<int64> old_sync_ids;
+
   // Free pointer for tab pool. Only those node id's, up to and including the
   // one indexed by the free pointer, are valid and free. The rest of the
   // |tab_syncid_pool_| is invalid because the nodes are in use.