GitLab

Added UMAs for:
1) The % of fullscreen video that is opened in portrait mode
2) The % of the video is suited for portrait mode
3) How long does a video play before user rotate the screen to landscape mode
4) How long video plays after user rotate the screen to landscape mode
5) How long does a video play before user rotate to portrait mode
6) The % of a video that the user switched from portrait to landscape mode

BUG=326572

Review URL: https://codereview.chromium.org/297773004

Cr-Commit-Position: refs/heads/master@{#293045}