📰 Use "> 320dp" instead of ">= 360dp" for regular layouts

Change the way the UiConfig thesholds are defined so that the switch
to small layouts is more restricted. The status bar height is
substracted from the screen height, which makes 360dp wide devices like
Pixel fall under the FLAT bucket when in landscape.

BUG=None

Review-Url: https://codereview.chromium.org/2703233002
Cr-Commit-Position: refs/heads/master@{#451624}