[CRX] Pass expected length of stream to viewer

To get a progress bar for POST/FTP requests in Chromium.
Fix wrong page being displayed when entering/exiting Presentation mode with zoom set to 'page-fit'
Remove the unnecessary this.buf in CCITTFaxStream.
Remove some unnecessary local variables.
Merge pull request #4229 from Rob--W/crx-stream-progress

Get progress bar for PDF streams in Chromium by passing the expected content length to the page
Fix spacebar scrolling in Firefox (4224 follow-up)
Merge pull request #4341 from Snuffleupagus/issue-4224-followup

Fix spacebar scrolling in Firefox (4224 follow-up)
Merge pull request #4292 from Snuffleupagus/issue-4232

Fix wrong page being displayed when entering/exiting Presentation mode with zoom set to 'page-fit'
Merge pull request #4331 from nnethercote/cleanups

Minor clean-ups