Crash fix in fileapi::FileSystemOperation::DidGetUsageAndQuotaAndRunTask

https://chromiumcodereview.appspot.com/10008047 introduced delete-with-inflight-tasks in Write sequence but I failed to convert this callback to use WeakPtr().

BUG=128178
TEST=manual test

Review URL: https://chromiumcodereview.appspot.com/10408006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@137635 0039d316-1c4b-4281-b951-d872f2087c98
void FileSystemOperation::DoWrite(scoped_ptr<net::URLRequest> blob_request) {
  int file_flags = base::PLATFORM_FILE_OPEN |
                   base::PLATFORM_FILE_WRITE |
                   base::PLATFORM_FILE_ASYNC;

  FileSystemOperationContext* write_context = new FileSystemOperationContext(
      operation_context_);
  FileSystemFileUtilProxy::CreateOrOpen(
      write_context, src_util_, src_path_, file_flags,
      base::Bind(&FileSystemOperation::OnFileOpenedForWrite,
                 weak_factory_.GetWeakPtr(),
                 base::Passed(&blob_request),
                 base::Owned(write_context)));
}

void FileSystemOperation::DoWrite(scoped_ptr<net::URLRequest> blob_request) {
  int file_flags = base::PLATFORM_FILE_OPEN |
                   base::PLATFORM_FILE_WRITE |
                   base::PLATFORM_FILE_ASYNC;

  FileSystemOperationContext* write_context = new FileSystemOperationContext(
      operation_context_);
  FileSystemFileUtilProxy::CreateOrOpen(
      write_context, src_util_, src_path_, file_flags,
      base::Bind(&FileSystemOperation::OnFileOpenedForWrite,
                 weak_factory_.GetWeakPtr(),
                 base::Passed(&blob_request),
                 base::Owned(write_context)));
}
