[Sync] Move some code into new class JsMutationEventObserver

chrome/browser/sync/syncable/syncable.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_SYNCABLE_SYNCABLE_H_
 #define CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_H_
 #pragma once
 
 #include <algorithm>
 #include <bitset>
@@ skipping 609 matching lines @@
                        tracked_objects::Location location,
                        WriterTag writer,
                        ImmutableEntryKernelMutationMap mutations);
   WriteTransactionInfo();
   ~WriteTransactionInfo();
 
   // Caller owns the return value.
   base::DictionaryValue* ToValue(size_t max_mutations_size) const;
 
   int64 id;
-  // TODO(akalin): Use Location when it becomes assignable.
+  // If tracked_objects::Location becomes assignable, we can use that
+  // instead.
   std::string location_string;
   WriterTag writer;
   ImmutableEntryKernelMutationMap mutations;
 };
 
 typedef
     browser_sync::Immutable<WriteTransactionInfo>
     ImmutableWriteTransactionInfo;
 
 // Caller owns the return value.
@@ skipping 605 matching lines @@
 bool IsLegalNewParent(BaseTransaction* trans, const Id& id, const Id& parentid);
 
 // This function sets only the flags needed to get this entry to sync.
 void MarkForSyncing(syncable::MutableEntry* e);
 
 }  // namespace syncable
 
 std::ostream& operator <<(std::ostream&, const syncable::Blob&);
 
 #endif  // CHROME_BROWSER_SYNC_SYNCABLE_SYNCABLE_H_