[Sync] Moved tab_node_id tracking to session object and improved foreign session garbage collection.

components/sync_sessions/synced_session.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_H_
 #define COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_H_
 
 #include <map>
+#include <set>
 #include <string>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "components/sessions/core/session_id.h"
 #include "components/sessions/core/session_types.h"
 #include "sync/protocol/session_specifics.pb.h"
 
 namespace sessions {
 struct SessionWindow;
@@ skipping 25 matching lines @@
   ~SyncedSession();
 
   // Unique tag for each session.
   std::string session_tag;
   // User-visible name
   std::string session_name;
 
   // Type of device this session is from.
   DeviceType device_type;
 
-  // Last time this session was modified remotely.
+  // Last time this session was modified remotely. This is the max of the header
+  // and all children tab mtimes.
   base::Time modified_time;
 
   // Map of windows that make up this session. Windowws are owned by the session
   // itself and free'd on destruction.
   SyncedWindowMap windows;
 
+  // All of the known to be valid tab node ids associated with this session.

[Nicolas Zea, 2016/04/12 20:38:03]

Why mention "known to be valid"?

Also "stored in the header" makes it sound like this data somehow gets taken and
pushed into the header node. Similarly, "assembled for all tabs" makes it sound
like the tabs are themselves using this data (rather than this data coming from
the tab nodes). Consider rephrasing?

[skym, 2016/04/12 22:12:14]

Yeah, I have no idea what I was thinking when I typed "known to be valid",
because I'm filtering out invalid tabs in LookupTabNodeIds(...).

Done.

[Nicolas Zea, 2016/04/14 18:17:25]

Much clearer, thanks!

+  // This is not stored in the header, but rather assembled for all tabs, both
+  // parented and orphaned.
+  std::set<int> tab_node_ids;
+
   // Converts the DeviceType enum value to a string. This is used
   // in the NTP handler for foreign sessions for matching session
   // types to an icon style.
   std::string DeviceTypeAsString() const {
     switch (device_type) {
       case SyncedSession::TYPE_WIN:
         return "win";
       case SyncedSession::TYPE_MACOSX:
         return "macosx";
       case SyncedSession::TYPE_LINUX:
@@ skipping 15 matching lines @@
   // does not create SessionTab protobufs.
   sync_pb::SessionHeader ToSessionHeader() const;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncedSession);
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_SESSIONS_SYNCED_SESSION_H_