Revert 6643 "Revert 6637 "Revert 6636 "Roll chromium_revision 28..."

Ha. Of course if won't work since a newer revision is required that pulls in the GN fix.

> Revert 6637 "Revert 6636 "Roll chromium_revision 280876:281479""
> 
> GN issue should be fixed in http://crrev.com/282138.
> 
> > Revert 6636 "Roll chromium_revision 280876:281479"
> > 
> > Still breaks GN bot.
> > 
> > > Roll chromium_revision 280876:281479
> > > 
> > > No significant DEPS changes in this roll, only some changes in how clang_format is downloaded. clang_format changes based on https://webrtc-codereview.appspot.com/20829004 which was reverted.
> > > 
> > > Review URL: https://webrtc-codereview.appspot.com/19929004
> > 
> > TBR=henrikg@webrtc.org
> > 
> > Review URL: https://webrtc-codereview.appspot.com/14909004
> 
> TBR=henrikg@webrtc.org
> 
> Review URL: https://webrtc-codereview.appspot.com/20899004

TBR=henrikg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/14919004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6644 4adac7df-926f-26a2-2b94-8c16560cd09d