sync: Add DeviceInfo protobuf and supporting code

sync/internal_api/sync_manager_impl.h

Index: sync/internal_api/sync_manager_impl.h
diff --git a/sync/internal_api/sync_manager_impl.h b/sync/internal_api/sync_manager_impl.h
index e315b2cff6ac67e28a9bfa6af9b3f352da273b44..e9832d40152651413548b3be638236341b93d59c 100644
--- a/sync/internal_api/sync_manager_impl.h
+++ b/sync/internal_api/sync_manager_impl.h
@@ -244,12 +244,6 @@ class SyncManagerImpl : public SyncManager,
                                 bool existed_before,
                                 bool exists_now);
 
-  // Internal callback used by GetSessionName.
-  // TODO(rlarocque): not currently called from anywhere. This should be
-  // hooked up to something once we start preserving device information again.
-  void UpdateSessionNameCallback(const std::string& chrome_version,
-                                 const std::string& session_name);
-
   // Called for every notification. This updates the notification statistics
   // to be displayed in about:sync.
   void UpdateNotificationInfo(