Tidy up app::response().

Follow-up from https://codereview.chromium.org/424883002/

- Remove some stray whitespace.
- Fix "else after return".
- Remove unused swResponse local.
- Treat unexpectedly large responses as errors.

BUG=
R=jun_fang@foxitsoftware.com

Review URL: https://codereview.chromium.org/423953002