Cleanup: return value and null-callback fixups on AsyncFileUtil interface

webkit/browser/fileapi/file_system_operation_context.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 WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_OPERATION_CONTEXT_H_
 #define WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_OPERATION_CONTEXT_H_
 
 #include "base/files/file_path.h"
 #include "base/supports_user_data.h"
 #include "base/threading/thread_checker.h"
@@ skipping 14 matching lines @@
 // multiple operations as far as those operations are supposed to share
 // the same context (e.g. use the same task runner, share the quota etc).
 // Note that the remaining quota bytes (allowed_bytes_growth) may be
 // updated during the execution of write operations.
 class WEBKIT_STORAGE_BROWSER_EXPORT_PRIVATE FileSystemOperationContext
     : public base::SupportsUserData {
  public:
   explicit FileSystemOperationContext(FileSystemContext* context);
 
   // Specifies |task_runner| which the operation is performed on.
+  // The backend of |task_runner| must outlive the IO thread.
   FileSystemOperationContext(FileSystemContext* context,
                              base::SequencedTaskRunner* task_runner);
 
   virtual ~FileSystemOperationContext();
 
   FileSystemContext* file_system_context() const {
     return file_system_context_.get();
   }
 
   // Updates the current remaining quota.
@@ skipping 73 matching lines @@
 
   // Used to check its setters are not called on arbitrary thread.
   base::ThreadChecker setter_thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystemOperationContext);
 };
 
 }  // namespace fileapi
 
 #endif  // WEBKIT_BROWSER_FILEAPI_FILE_SYSTEM_OPERATION_CONTEXT_H_