Change code review host to Chromium's Rietveld.

Since WebRTC's codereview instance at webrtc-codereview.appspot.com
is going to be read-only, libyuv needs to switch to Chromium's instance.

Also update the ViewVC URL to match the Git repo that is now the
master repo.

After this CL has landed, existing Git branches will continue to remember which Rietveld URL they uploaded to.
To reset a branch and re-upload a new CL to the new instance, do like this:
git cl issue 0
git pull --rebase origin master
git cl upload

BUG=libyuv:450
R=fbarchard@chromium.org

Review URL: https://codereview.chromium.org/1154893003 .

codereview.settings

 # This file is used by gcl to get repository specific information.
-# The LibYuv code review is via WebRtc's code review
-CODE_REVIEW_SERVER: webrtc-codereview.appspot.com
+CODE_REVIEW_SERVER: codereview.chromium.org
 #CC_LIST:
-VIEW_VC: https://code.google.com/p/libyuv/source/detail?r=
+VIEW_VC: https://chromium.googlesource.com/libyuv/libyuv/+/
 #STATUS:
 FORCE_HTTPS_COMMIT_URL: True
 PROJECT: libyuv