Don't always fully repaint on viewport resize

LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt

Index: LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt
diff --git a/LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt b/LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt
index c95d32ceb5595ee28edb8e09cbc8cbed9cd50c94..e4a4656e3114a10e3eac33fe8d5c4d527c4dcea6 100644
--- a/LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt
+++ b/LayoutTests/fast/repaint/window-resize-viewport-percent-expected.txt
@@ -7,9 +7,10 @@ width: 200 height: 300
       (contentsOpaque 1)
       (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)
+        (rect 20.00 0.00 10.00 30.00)
+        (rect 0.00 20.00 30.00 10.00)
+        (rect 0.00 0.00 20.00 20.00)
+        (rect 0.00 0.00 30.00 30.00)
       )
     )
   )
@@ -39,9 +40,11 @@ width: 300 height: 250
       (contentsOpaque 1)
       (drawsContent 1)
       (repaint rects
-        (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)
+        (rect 25.00 0.00 5.00 30.00)
+        (rect 0.00 25.00 30.00 5.00)
+        (rect 0.00 0.00 30.00 30.00)
+        (rect 0.00 0.00 25.00 25.00)
+        (rect 0.00 250.00 300.00 50.00)
       )
     )
   )