GitLab

- remove some window properties that had been used for theming
- remove dead member variable
- update comments
- use remove_standard_frame / kRemoveStandardFrame_InitProperty instead
  of kDisableImmersive_InitProperty for Mash browser windows

Bug: 887051
Change-Id: Ia7d64acebca600354162be9560bc64761bd3570e
Reviewed-on: https://chromium-review.googlesource.com/c/1255924Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596357}