Reland "Unifies ScrollView and RenderLayer to use non-shi..."

LayoutTests/platform/chromium-linux/virtual/softwarecompositing/overflow/scrolling-content-clip-to-viewport-expected.txt

 (GraphicsLayer
   (bounds 800.00 600.00)
   (children 1
     (GraphicsLayer
       (bounds 800.00 600.00)
       (contentsOpaque 1)
       (children 1
         (GraphicsLayer
           (bounds 320.00 340.00)
           (children 4
             (GraphicsLayer
-              (bounds 320.00 340.00)
+              (bounds 305.00 325.00)
               (children 1
                 (GraphicsLayer
                   (bounds 305.00 1224.00)
                   (drawsContent 1)
                 )
               )
             )
             (GraphicsLayer
               (position 0.00 325.00)
               (bounds 305.00 15.00)
               (drawsContent 1)
             )
             (GraphicsLayer
               (position 305.00 0.00)
               (bounds 15.00 325.00)
               (drawsContent 1)
             )
             (GraphicsLayer
               (position 305.00 325.00)
               (bounds 15.00 15.00)
               (drawsContent 1)
             )
           )
         )
       )
     )
   )
 )