Instead of using a simple ImageView for the icon, this uses the platform
layout/action_bar_home which uses a custom class to position and resize
the icon (and also supports the Up icon that we don't yet support).
This ensures that the icon is properly positionned and sized like
on devices.
(cherry picked from commit 7396348dfcfb45b7ad055f4c18cabbe5e8270d26)
Change-Id: Ifd3bc318089b70ba843519523e366e59d434e919
331bb0c393