Enforces trailing spaces
Merge pull request #3428 from yurydelendik/enforce-trailing

Enforces trailing spaces
[Chrome extension] Added JSDocs to pdfHandler.js

And a small refactor to reduce the LOC in the onHeadersReceived
callback, to improve the readability of the code.
[CRX] Don't intercept download of PDF attachment

Fixes #3426
Download PDF from cache for non-Firefox add-on

This feature relies on URL.createObjectURL, which is supported by
- Firefox 4
- Chrome 8
- Opera 15
- Internet Explorer 10

If the feature is missing, it falls back to downloading from the server.

The environment-specific code are put in ifdef's. Two methods are
defined:
- noData
  This function is used as a fallback in case of failure, it triggers
  a download directly from the server.
- triggerSaveAs(String url, optional String blob)
  This function attempts to show a Save As dialog for a given URL.
  It attempts to use the a.download attribute, if available, and
  falls back to window.open(<url>, '_parent') if unavailable.

See also http://caniuse.com/download