[SyncFS] [Refactoring] Change RemovePrefix() to return bool

chrome/browser/sync_file_system/drive_backend/drive_backend_util.h

 // Copyright 2013 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_FILE_SYSTEM_DRIVE_BACKEND_DRIVE_BACKEND_UTIL_H_
 #define CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_DRIVE_BACKEND_UTIL_H_
 
 #include <string>
 
 #include "base/bind.h"
@@ skipping 32 matching lines @@
 
 bool HasFileAsParent(const FileDetails& details, const std::string& file_id);
 
 bool IsAppRoot(const FileTracker& tracker);
 
 std::string GetTrackerTitle(const FileTracker& tracker);
 
 SyncStatusCode GDataErrorCodeToSyncStatusCode(
     google_apis::GDataErrorCode error);
 
-std::string RemovePrefix(const std::string& str, const std::string& prefix);
+// Returns true if |str| starts with |prefix|, and removes |prefix| from |str|.
+// If |out| is not NULL, the result is stored in it.
+bool RemovePrefix(const std::string& str, const std::string& prefix,
+                  std::string* out);
 
 template <typename Src, typename Dest>
 void AppendContents(const Src& src, Dest* dest) {
   dest->insert(dest->end(), src.begin(), src.end());
 }
 
 template <typename Container>
 const typename Container::mapped_type& LookUpMap(
     const Container& container,
     const typename Container::key_type& key,
@@ skipping 14 matching lines @@
 base::Callback<R()> CreateComposedFunction(
     const base::Callback<T()>& g,
     const base::Callback<R(S)>& f) {
   return base::Bind(&ComposeFunction<R, S, T>, g, f);
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system
 
 #endif  // CHROME_BROWSER_SYNC_FILE_SYSTEM_DRIVE_BACKEND_DRIVE_BACKEND_UTIL_H_