This introduces Chromium 39 as the new stable version along with a bunch
of fixes.
Fixes#2799, particularily the PDF plugin, which now is open source and
thus no longer an issue.
Also fixes#3219 and merges #2906, so we no longer get a crash while
trying to bring up the print preview dialog.
Thanks to @edwtjo for the CUPS version bump.
* chromium: Switch to use open-source PDF plugin.
* cups: bump 1.5.4 -> 1.7.5
* chromium: Allow env vars for passing plugin paths.
* chromium: Update all channels to latest versions.
* protobuf: Clean up and update to version 2.6.1.
392a4c0a26