Roll chromium_revision 280876:281094

No significant DEPS changes in this roll, only some changes
in how clang_format is downloaded.

BUG=
TEST=Local testing as trybots currently cannot handle DEPS changes properly.
R=niklas.enbom@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/20829004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6597 4adac7df-926f-26a2-2b94-8c16560cd09d