This is the IPC and bits of the browser backend for FileWriter. The rest of...

chrome/browser/file_system/file_system_dispatcher_host.h

 // Copyright (c) 2010 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_FILE_SYSTEM_FILE_SYSTEM_DISPATCHER_HOST_H_
 #define CHROME_BROWSER_FILE_SYSTEM_FILE_SYSTEM_DISPATCHER_HOST_H_
 
 #include "base/basictypes.h"
 #include "base/file_util.h"
 #include "base/id_map.h"
 #include "base/nullable_string16.h"
 #include "base/process.h"
 #include "base/platform_file.h"
 #include "base/scoped_callback_factory.h"
 #include "base/ref_counted.h"
 #include "chrome/common/render_messages.h"
 #include "webkit/fileapi/file_system_operation.h"
 
 class FileSystemHostContext;
+class GURL;
 class HostContentSettingsMap;
 class Receiver;
 class ResourceMessageFilter;
 
 class FileSystemDispatcherHost
     : public base::RefCountedThreadSafe<FileSystemDispatcherHost> {
  public:
   FileSystemDispatcherHost(IPC::Message::Sender* sender,
                            FileSystemHostContext* file_system_host_context,
                            HostContentSettingsMap* host_content_settings_map);
@@ skipping 12 matching lines @@
               const FilePath& dest_path);
   void OnRemove(int request_id, const FilePath& path);
   void OnReadMetadata(int request_id, const FilePath& path);
   void OnCreate(int request_id,
                 const FilePath& path,
                 bool exclusive,
                 bool is_directory,
                 bool recursive);
   void OnExists(int request_id, const FilePath& path, bool is_directory);
   void OnReadDirectory(int request_id, const FilePath& path);
+  void OnWrite(int request_id,
+               const FilePath& path,
+               const GURL& blob_url,
+               int64 offset);
+  void OnTruncate(int request_id, const FilePath& path, int64 length);
+  void OnCancel(int request_id, int request_to_cancel);
   void Send(IPC::Message* message);
   void RemoveCompletedOperation(int request_id);
 
  private:
   // Creates a new FileSystemOperation.
   fileapi::FileSystemOperation* GetNewOperation(int request_id);
 
   // Checks the validity of a given |path|. Returns true if the given |path|
   // is valid as a path for FileSystem API. Otherwise it sends back a
   // security error code to the dispatcher and returns false.
@@ skipping 13 matching lines @@
   scoped_refptr<HostContentSettingsMap> host_content_settings_map_;
 
   // Keeps ongoing file system operations.
   typedef IDMap<fileapi::FileSystemOperation, IDMapOwnPointer> OperationsMap;
   OperationsMap operations_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystemDispatcherHost);
 };
 
 #endif  // CHROME_BROWSER_FILE_SYSTEM_FILE_SYSTEM_DISPATCHER_HOST_H_