[Home] Position app menu based on location of anchor view

If the anchor view for the app menu is at the top of the screen,
the menu should have a negative vertical offset so that it covers
the anchor view. If the anchor view is at the bottom of the screen,
the menu should have a positive vertical offset so that it covers
the anchor view.

BUG=703317

Review-Url: https://codereview.chromium.org/2761033002
Cr-Commit-Position: refs/heads/master@{#458203}
1 file changed