Implement SandboxFileWriter and rewrite FileWriterDelegate to use it

webkit/fileapi/file_writer.h

Index: webkit/fileapi/file_writer.h
diff --git a/webkit/fileapi/file_writer.h b/webkit/fileapi/file_writer.h
index c28c5d9f99053617f59749111344c47980877a1b..1b56c194dc968b712f5d0e041a692e1f235e0c1d 100644
--- a/webkit/fileapi/file_writer.h
+++ b/webkit/fileapi/file_writer.h
@@ -31,6 +31,13 @@ class FileWriter {
   // callback will be run on the thread where Write() was called when the write
   // has completed.
   //
+  // This errors out (either synchronously or via callback) with:
+  //   net::ERR_FILE_NOT_FOUND: When the target file is not found.
+  //   net::ERR_ACCESS_DENIED: When the target file is a directory or
+  //      the writer has no permission on the file.
+  //   net::ERR_FILE_NO_SPACE: When the write will result in out of quota
+  //      or there is not enough room left on the disk.
+  //
   // It is invalid to call Write while there is an in-flight async operation.
   virtual int Write(net::IOBuffer* buf, int buf_len,
                     const net::CompletionCallback& callback) = 0;
@@ -53,4 +60,3 @@ class FileWriter {
 }  // namespace fileapi
 
 #endif  // WEBKIT_FILEAPI_FILE_WRITER_H_
-