sync: don't notify from ~BaseTransaction if the writer is INVALID.

chrome/chrome.gyp

 # 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.
 {
   'variables': {
     'chromium_code': 1,
 
     'variables': {
       'version_py_path': 'tools/build/version.py',
       'version_path': 'VERSION',
@@ skipping 456 matching lines @@
         'browser/sync/syncable/syncable.h',
         'browser/sync/syncable/syncable_changes_version.h',
         'browser/sync/syncable/syncable_columns.h',
         'browser/sync/syncable/syncable_id.cc',
         'browser/sync/syncable/syncable_id.h',
         'browser/sync/syncable/syncable_enum_conversions.cc',
         'browser/sync/syncable/syncable_enum_conversions.h',
         'browser/sync/syncable/transaction_observer.h',
         'browser/sync/util/cryptographer.cc',
         'browser/sync/util/cryptographer.h',
-        'browser/sync/util/dbgq.h',
         'browser/sync/util/extensions_activity_monitor.cc',
         'browser/sync/util/extensions_activity_monitor.h',
         'browser/sync/util/immutable.h',
         'browser/sync/util/logging.cc',
         'browser/sync/util/logging.h',
         'browser/sync/util/nigori.cc',
         'browser/sync/util/nigori.h',
         'browser/sync/util/oauth.cc',
         'browser/sync/util/oauth.h',
         'browser/sync/util/sqlite_utils.cc',
@@ skipping 815 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ]},  # 'targets'
     ],  # OS=="win"
   ],  # 'conditions'
 }