GitLab

Layerless windows are only used in unit tests today, and add
complexity in that a NativeWidgetAura can not rely on there
being a layer present. In practice, having a layer per Window
is not unreasonable overhead, and is simpler. The way to render
something into the same layer is to use a separate View instead
of a separate Window.

R=sky
BUG=466426

Review URL: https://codereview.chromium.org/1050713002

Cr-Commit-Position: refs/heads/master@{#323610}