Animate showing / hiding the location bar for bookmark apps.

      Bookmark apps no longer toggle whether they support the location bar
via the browser features system, which didn't seem correct. Instead they
support the location bar feature always but change how the location
bar's height to bring it into and out of view.

This change also introduces a BookmarkAppBrowserController class to
encapsulate all the logic for bookmark apps to modify the browser UI.

BUG=463405

Review URL: https://codereview.chromium.org/1036173002

Cr-Commit-Position: refs/heads/master@{#324020}