[Sync] Add plumbing of context from client to server

sync/internal_api/public/write_transaction.h

 // Copyright 2012 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 SYNC_INTERNAL_API_PUBLIC_WRITE_TRANSACTION_H_
 #define SYNC_INTERNAL_API_PUBLIC_WRITE_TRANSACTION_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "sync/base/sync_export.h"
@@ skipping 25 matching lines @@
   // if not after transaction is closed. This constructor is used for model
   // types that support embassy data.
   WriteTransaction(const tracked_objects::Location& from_here,
                    UserShare* share, int64* transaction_version);
   virtual ~WriteTransaction();
 
   // Provide access to the syncable transaction from the API WriteNode.
   virtual syncable::BaseTransaction* GetWrappedTrans() const OVERRIDE;
   syncable::WriteTransaction* GetWrappedWriteTrans() { return transaction_; }
 
+  // Set's a |type|'s local context. Does not affect any individual entities.
+  void SetDataTypeContext(ModelType type, const std::string& context);
+
  protected:
   WriteTransaction() {}
 
   void SetTransaction(syncable::WriteTransaction* trans) {
     transaction_ = trans;
   }
 
  private:
   void* operator new(size_t size);  // Transaction is meant for stack use only.
 
   // The underlying syncable object which this class wraps.
   syncable::WriteTransaction* transaction_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteTransaction);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_WRITE_TRANSACTION_H_