[USS] Show USS counters in about:sync page

components/sync/driver/sync_frontend.h

 // Copyright 2014 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_DRIVER_SYNC_FRONTEND_H_
 #define COMPONENTS_SYNC_DRIVER_SYNC_FRONTEND_H_
 
 #include <string>
 
 #include "components/sync/base/model_type.h"
@@ skipping 61 matching lines @@
       const syncer::CommitCounters& counters) = 0;
 
   // Called when we receive an updated update counter for a directory type.
   //
   // Disabled by default.  Enable by calling
   // EnableDirectoryTypeDebugInfoForwarding() on the backend.
   virtual void OnDirectoryTypeUpdateCounterUpdated(
       syncer::ModelType type,
       const syncer::UpdateCounters& counters) = 0;
 
-  // Called when we receive an updated status counter for a directory type.
+  // Called when we receive an updated status counter for a datatype which is

[pavely, 2016/09/30 00:01:51]

I don't think this comment needs to elaborate kinds of datatypes.
Simply "Called when we receive an updated status counter for a datatype." should
be enough.

[Gang Wu, 2016/10/01 07:14:09]

Done.

+  // directory type or Unified Sync and Storage.
   //
   // Disabled by default.  Enable by calling
   // EnableDirectoryTypeDebugInfoForwarding() on the backend.
-  virtual void OnDirectoryTypeStatusCounterUpdated(
+  virtual void OnDatatypeStatusCounterUpdated(
       syncer::ModelType type,
-      const syncer::StatusCounters& counters) = 0;
+      std::unique_ptr<syncer::StatusCounters> counters) = 0;
 
   // The status of the connection to the sync server has changed.
   virtual void OnConnectionStatusChange(syncer::ConnectionStatus status) = 0;
 
   // The syncer requires a passphrase to decrypt sensitive updates. This is
   // called when the first sensitive data type is setup by the user and anytime
   // the passphrase is changed by another synced client. |reason| denotes why
   // the passphrase was required. |pending_keys| is a copy of the
   // cryptographer's pending keys to be passed on to the frontend in order to
   // be cached.
@@ skipping 39 matching lines @@
   // |nigori_state| contains the new (post custom passphrase) encryption keys
   // and can be used to restore SyncEncryptionHandler's state across sync
   // backend instances. See also SyncEncryptionHandlerImpl::RestoreNigori.
   virtual void OnLocalSetPassphraseEncryption(
       const syncer::SyncEncryptionHandler::NigoriState& nigori_state) = 0;
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_DRIVER_SYNC_FRONTEND_H_