GitLab

- Drag now works again.
- Ensure the nested run loop gets torn down on errors.
- Adds logs of dvlogs for debugging when needed.
- Moves registration of aura components to //ui/aura/.

BUG=699235,665077

Review-Url: https://codereview.chromium.org/2739213003
Cr-Commit-Position: refs/heads/master@{#456193}