Issue repaints for RenderLayers that get new composited backings after

LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt

Index: LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
diff --git a/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt b/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
index ce78e7591ec7ec61f1ba9b842789def17bd02aff..5421b2fce265b90373b2411fa5cc50524eb88fb3 100644
--- a/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
+++ b/LayoutTests/compositing/squashing/add-remove-squashed-layers-expected.txt
@@ -56,8 +56,7 @@ CASE 2, overlap3 gets added:
               (bounds 260.00 260.00)
               (drawsContent 1)
               (repaint rects
-                (rect 160.00 160.00 20.00 20.00)
-                (rect 140.00 140.00 40.00 40.00)
+                (rect 160.00 160.00 100.00 100.00)
                 (rect 80.00 80.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
               )
@@ -160,10 +159,10 @@ CASE 5, overlap2 gets added back:
               (bounds 180.00 180.00)
               (drawsContent 1)
               (repaint rects
+                (rect 80.00 80.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
-                (rect 0.00 0.00 20.00 20.00)
               )
             )
           )
@@ -200,11 +199,10 @@ CASE 6, overlap1 gets added back, and overlap3 gets removed:
               (drawsContent 1)
               (repaint rects
                 (rect 80.00 80.00 100.00 100.00)
+                (rect 80.00 80.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
                 (rect 0.00 0.00 100.00 100.00)
-                (rect 0.00 0.00 20.00 20.00)
-                (rect 0.00 0.00 20.00 20.00)
               )
             )
           )