Work around inconsistent views in RelativeLayout.onMeasure()

Previously, RelativeLayout's measure pass could crash if the view's
children were modified without calling requestLayout() prior to the
next measure pass. This avoids the issue by only looking at the most
recent set of sorted views and preserves the previous behavior where
onMeasure() could return incorrect data.

Bug: 21123292
Change-Id: If471d071d1d2e2729cf13854d95b1f517c1fe73a