Unifies ScrollView and RenderLayer to use non-shifted [minPos, maxPos] scroll offset

LayoutTests/virtual/gpu/compositedscrolling/overflow/overflow-auto-with-touch-expected.txt

 (GraphicsLayer
   (bounds 800.00 600.00)
   (children 1
     (GraphicsLayer
       (bounds 800.00 600.00)
       (contentsOpaque 1)
       (children 1
         (GraphicsLayer
           (position 8.00 8.00)
           (bounds 300.00 300.00)
           (children 4
             (GraphicsLayer
-              (bounds 300.00 300.00)
+              (bounds 285.00 285.00)
               (children 1
                 (GraphicsLayer
                   (bounds 1000.00 1000.00)
                   (drawsContent 1)
                 )
               )
             )
             (GraphicsLayer
               (position 0.00 285.00)
               (bounds 285.00 15.00)
               (drawsContent 1)
             )
             (GraphicsLayer
               (position 285.00 0.00)
               (bounds 15.00 285.00)
               (drawsContent 1)
             )
             (GraphicsLayer
               (position 285.00 285.00)
               (bounds 15.00 15.00)
               (drawsContent 1)
             )
           )
         )
       )
     )
   )
 )