Ensure the checkout is updated _before_ reading the current revision from the DEPS file. This will avoid errors when a checkout is not up to date, as updating happened after reading the revision before this change. BUG=webrtc:4688 R=phoglund@webrtc.org Review URL: https://codereview.webrtc.org/1361923004 . Cr-Commit-Position: refs/heads/master@{#10071}