Don't always fully repaint on viewport resize

LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt

Index: LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt
diff --git a/LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt b/LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt
index ca38c87a0e25674ddad39e8535e21a322d53dd30..d79c1f7f5e3acc4a1394b459ff66c0a3664d505b 100644
--- a/LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt
+++ b/LayoutTests/fast/repaint/window-resize-fixed-center-background-image-expected.txt
@@ -7,8 +7,6 @@
       (drawsContent 1)
       (repaint rects
         (rect 0.00 0.00 200.00 200.00)
-        (rect 0.00 0.00 200.00 200.00)
-        (rect 0.00 0.00 200.00 200.00)
       )
     )
   )
@@ -22,8 +20,6 @@
       (drawsContent 1)
       (repaint rects
         (rect 0.00 0.00 200.00 300.00)
-        (rect 0.00 0.00 200.00 300.00)
-        (rect 0.00 0.00 200.00 300.00)
       )
     )
   )
@@ -36,9 +32,8 @@
       (contentsOpaque 1)
       (drawsContent 1)
       (repaint rects
+        (rect 0.00 250.00 300.00 50.00)
         (rect 0.00 0.00 300.00 300.00)
-        (rect 0.00 0.00 300.00 300.00)
-        (rect 0.00 0.00 300.00 250.00)
       )
     )
   )
@@ -51,9 +46,8 @@
       (contentsOpaque 1)
       (drawsContent 1)
       (repaint rects
+        (rect 250.00 0.00 50.00 250.00)
         (rect 0.00 0.00 300.00 250.00)
-        (rect 0.00 0.00 300.00 250.00)
-        (rect 0.00 0.00 250.00 250.00)
       )
     )
   )