sync: Make BaseNode lookup-related Init functions return specific failures.

chrome/browser/sync/internal_api/read_node.h

 // Copyright (c) 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 CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_
 #define CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_
 #pragma once
 
 #include <string>
 
@@ skipping 10 matching lines @@
  public:
   // Create an unpopulated ReadNode on the given transaction.  Call some flavor
   // of Init to populate the ReadNode with a database entry.
   explicit ReadNode(const BaseTransaction* transaction);
   virtual ~ReadNode();
 
   // A client must use one (and only one) of the following Init variants to
   // populate the node.
 
   // BaseNode implementation.
-  virtual bool InitByIdLookup(int64 id) OVERRIDE;
-  virtual bool InitByClientTagLookup(syncable::ModelType model_type,
-                                     const std::string& tag) OVERRIDE;
+  virtual InitByLookupResult InitByIdLookup(int64 id) OVERRIDE;
+  virtual InitByLookupResult InitByClientTagLookup(
+      syncable::ModelType model_type,
+      const std::string& tag) OVERRIDE;
 
   // There is always a root node, so this can't fail.  The root node is
   // never mutable, so root lookup is only possible on a ReadNode.
   void InitByRootLookup();
 
   // Each server-created permanent node is tagged with a unique string.
   // Look up the node with the particular tag.  If it does not exist,
   // return false.
-  bool InitByTagLookup(const std::string& tag);
+  InitByLookupResult InitByTagLookup(const std::string& tag);
 
   // Implementation of BaseNode's abstract virtual accessors.
   virtual const syncable::Entry* GetEntry() const OVERRIDE;
   virtual const BaseTransaction* GetTransaction() const OVERRIDE;
 
  protected:
   ReadNode();
 
  private:
   void* operator new(size_t size);  // Node is meant for stack use only.
 
   // The underlying syncable object which this class wraps.
   syncable::Entry* entry_;
 
   // The sync API transaction that is the parent of this node.
   const BaseTransaction* transaction_;
 
   DISALLOW_COPY_AND_ASSIGN(ReadNode);
 };
 
 }  // namespace sync_api
 
 #endif  // CHROME_BROWSER_SYNC_INTERNAL_API_READ_NODE_H_