GitLab

- StartOverview() should return true if enter overview successfully,
false otherwise
- EndOverview() should return true if end overview successfully, false
otherwise
- Other small refactorings

No functionality change in this CL.

Bug: None
Change-Id: I47fcf479bda3d51da98ee693e0a5acbe51f80c1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1785625
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694964}