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

webkit/tools/test_shell/simple_file_system.cc

Index: webkit/tools/test_shell/simple_file_system.cc
===================================================================
--- webkit/tools/test_shell/simple_file_system.cc	(revision 60387)
+++ webkit/tools/test_shell/simple_file_system.cc	(working copy)
@@ -92,6 +92,10 @@
     file_system_->RemoveCompletedOperation(request_id_);
   }
 
+  virtual void DidWrite(int64, bool, fileapi::FileSystemOperation*) {
+    NOTREACHED();
+  }
+
  private:
   SimpleFileSystem* file_system_;
   WebFileSystemCallbacks* callbacks_;