Avoid requiring a recalc to update compositing state for iframes

LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt

Index: LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt
diff --git a/LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt b/LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt
index fecf5a6f47621a833514bf8405b73d0653bab1cb..f506a0bce384235942ac3aa72109fe2af06b9c9a 100644
--- a/LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt
+++ b/LayoutTests/platform/mac/fast/overflow/scrollRevealButton-expected.txt
@@ -9,34 +9,35 @@ layer at (0,0) size 785x1188
         RenderText {#text} at (0,0) size 0x0
       RenderBlock {DIV} at (0,18) size 769x500
       RenderBlock (anonymous) at (0,518) size 769x154
-        RenderPartObject {IFRAME} at (0,0) size 304x154 [border: (2px inset #EEEEEE)]
-          layer at (0,0) size 308x316
-            RenderView at (0,0) size 285x135
-          layer at (0,0) size 285x316
-            RenderBlock {HTML} at (0,0) size 285x316
-              RenderBody {BODY} at (8,8) size 269x300
-          layer at (8,8) size 300x300 clip at (8,8) size 285x300 scrollY 543 scrollHeight 1268
-            RenderBlock {DIV} at (0,0) size 300x300
-              RenderBlock (anonymous) at (0,0) size 285x18
-                RenderText {#text} at (0,0) size 88x18
-                  text run at (0,0) width 88: "overflow:auto"
-              RenderBlock {DIV} at (0,18) size 285x600
-              RenderBlock {DIV} at (0,768) size 285x500
-          layer at (8,83) size 150x150 clip at (8,83) size 135x150 scrollY 472 scrollHeight 858
-            RenderBlock {DIV} at (0,618) size 150x150
-              RenderBlock (anonymous) at (0,0) size 135x18
-                RenderText {#text} at (0,0) size 88x18
-                  text run at (0,0) width 88: "overflow:auto"
-              RenderBlock {DIV} at (0,18) size 135x500
-              RenderBlock (anonymous) at (0,518) size 135x40
-                RenderBR {BR} at (0,0) size 0x18
-                RenderButton {INPUT} at (2,20) size 50.97x18 [bgcolor=#C0C0C0]
-                  RenderBlock (anonymous) at (8,2.50) size 34.97x13
-                    RenderText {#text} at (0,0) size 35x13
-                      text run at (0,0) width 35: "Button"
-                RenderText {#text} at (0,0) size 0x0
-              RenderBlock {DIV} at (0,558) size 135x300
         RenderText {#text} at (0,0) size 0x0
       RenderBlock {DIV} at (0,672) size 769x500
+layer at (8,526) size 304x154
+  RenderPartObject {IFRAME} at (0,0) size 304x154 [border: (2px inset #EEEEEE)]
+    layer at (0,0) size 308x316
+      RenderView at (0,0) size 285x135
+    layer at (0,0) size 285x316
+      RenderBlock {HTML} at (0,0) size 285x316
+        RenderBody {BODY} at (8,8) size 269x300
+    layer at (8,8) size 300x300 clip at (8,8) size 285x300 scrollY 543 scrollHeight 1268
+      RenderBlock {DIV} at (0,0) size 300x300
+        RenderBlock (anonymous) at (0,0) size 285x18
+          RenderText {#text} at (0,0) size 88x18
+            text run at (0,0) width 88: "overflow:auto"
+        RenderBlock {DIV} at (0,18) size 285x600
+        RenderBlock {DIV} at (0,768) size 285x500
+    layer at (8,83) size 150x150 clip at (8,83) size 135x150 scrollY 472 scrollHeight 858
+      RenderBlock {DIV} at (0,618) size 150x150
+        RenderBlock (anonymous) at (0,0) size 135x18
+          RenderText {#text} at (0,0) size 88x18
+            text run at (0,0) width 88: "overflow:auto"
+        RenderBlock {DIV} at (0,18) size 135x500
+        RenderBlock (anonymous) at (0,518) size 135x40
+          RenderBR {BR} at (0,0) size 0x18
+          RenderButton {INPUT} at (2,20) size 50.97x18 [bgcolor=#C0C0C0]
+            RenderBlock (anonymous) at (8,2.50) size 34.97x13
+              RenderText {#text} at (0,0) size 35x13
+                text run at (0,0) width 35: "Button"
+          RenderText {#text} at (0,0) size 0x0
+        RenderBlock {DIV} at (0,558) size 135x300
 scrolled to 0,4
 frame 'fr' scrolled to 0,91