Refactor ViewGroup.drawChild() into View.draw()

Some of the ongoing and upcoming jank work involves having
Views optimize their rendering. For example, it would be more
efficient for native display lists to be able to redraw themselves with
updated transform/alpha properties than it would be to do it the
way we do now, which causes view hierarchy invalidation and display
list recreation.

In order to do this, we need to push more intelligence for view
rendering into the Views themselves, rather than the complicated
mechanism we have now of ViewGroup handling some View properties
(transforms and alpha) and the Views handling the rest of their
rendering.

The first step toward this is to take the current drawChild() method
and push it into a new, package-private method in View that does the
same thing.

Future checkins will refactor the code further, simplifying it and
eventually optimizing around view property changes.

Change-Id: Id44b94536fc3ff80b474db7ef06862f4f51eedce