Instead of fitting system windows as before, DragLayer now
lays out under the system windows.
DragLayer will simply add the system window insets to each
child's layout margins by default. e.g. for Hotseat, Page
Indicators, QSB, Search Overlay.
Children that want to use the full viewport can declare so
by implementing a new Insettable interface. System window
insets will be passed to Insettable#setInsets(insets) and
the child can do what it wants with them.
Currently, two of DragLayer's children implement Insettable:
1) Workspace (for the -1 screen).
Full screen pages are given the entire viewport, paged
view offsets modified to end up in the right place now
that the viewport is larger (the full screen height).
Non-full screen pages like the normal icon pages simply
apply the insets to end up in the same place they did
NowClientCardsView uses the full viewport, applying the
insets as padding. Will want to better take advantage
of this new real estate in a future CL.
2) All Apps (AppsCustomizeTabHost).
Applies the insets as layout margin one level down, so that
the bar area is opaque during the transition, but visually
the content lands in the same place.
(Also add db_files to .gitignore to ignore the output of the