Revert the revert. This change was not the cause of the failures, so relanding.

chrome/browser/sync/internal_api/sync_manager.h

 // Copyright (c) 2011 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 CHROME_BROWSER_SYNC_INTERNAL_API_SYNC_MANAGER_H_
 #define CHROME_BROWSER_SYNC_INTERNAL_API_SYNC_MANAGER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 143 matching lines @@
     int empty_get_updates;
 
     // Count of useless and useful syncs we perform.
     int useless_sync_cycles;
     int useful_sync_cycles;
 
     // Encryption related.
     syncable::ModelTypeSet encrypted_types;
     bool cryptographer_ready;
     bool crypto_has_pending_keys;
+
+    // The unique identifer for this client.
+    std::string unique_id;
   };
 
   // An interface the embedding application implements to be notified
   // on change events.  Note that these methods may be called on *any*
   // thread.
   class ChangeDelegate {
    public:
     // Notify the delegate that changes have been applied to the sync model.
     //
     // This will be invoked on the same thread as on which ApplyChanges was
@@ skipping 424 matching lines @@
 syncable::ModelTypeSet GetTypesWithEmptyProgressMarkerToken(
     const syncable::ModelTypeSet types,
     sync_api::UserShare* share);
 
 // Returns the string representation of a PassphraseRequiredReason value.
 std::string PassphraseRequiredReasonToString(PassphraseRequiredReason reason);
 
 }  // namespace sync_api
 
 #endif  // CHROME_BROWSER_SYNC_INTERNAL_API_SYNC_MANAGER_H_