ViewRootImpl: More careful draw accounting.

The strategy of beginning the count at 1 isn't enough
and we need to explicitly debt each request to report
draw. Imagine the case where a ViewRootImpl reports draw
multiple times, while we are waiting for a SurfaceView draw
completion callback. Without the explicit draw debt, the ViewRoot
would be counted as drawing for the SurfaceView and we could
notify the WM too early.

Test: Open Chrome a few hundred times. go/wm-smoke.
Bug: 38324871
Change-Id: I5762a98d1cc808125033ba3d1db8a3ea39a9e071