Roll chromium_revision ea769fd..6455c69 (re-land)

Mainly to pick up https://codereview.chromium.org/552013004

Summary of changes (git diff ea769fd..6455c69 DEPS):
* third_party/libvpx ceebbcc0..d95585f
* third_party/swarming e7d8b98..14b5fd82
* tools/gyp 1972:1973

TBR=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/22349004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7139 4adac7df-926f-26a2-2b94-8c16560cd09d