Make View#computeOpaqueFlags recognize OUTSIDE_OVERLAY scrollbars

While the inset scrollbars may change padding and how backgrounds are
drawn such that an otherwise opaque view is no longer opaque. However,
OUTSIDE_OVERLAY scrollbars don't change the padding and should not
affect the determination of opacity.

Change-Id: I8c0c1408aeb540813de3351f0c0d1ad12ba5919c