Avoid requiring a recalc to update compositing state for iframes

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

Index: LayoutTests/platform/win/fast/overflow/scrollRevealButton-expected.txt
diff --git a/LayoutTests/platform/win/fast/overflow/scrollRevealButton-expected.txt b/LayoutTests/platform/win/fast/overflow/scrollRevealButton-expected.txt
index 9ba6a58bc18422459ed99f5a9b318a9ab1a36a2c..332a46104b71e4c1ecb24e4c1b3da40a3abd60c8 100644
--- a/LayoutTests/platform/win/fast/overflow/scrollRevealButton-expected.txt
+++ b/LayoutTests/platform/win/fast/overflow/scrollRevealButton-expected.txt
@@ -9,34 +9,35 @@ layer at (0,0) size 785x1190
         RenderText {#text} at (0,0) size 0x0
       RenderBlock {DIV} at (0,20) size 769x500
       RenderBlock (anonymous) at (0,520) 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 545 scrollHeight 1270
-            RenderBlock {DIV} at (0,0) size 300x300
-              RenderBlock (anonymous) at (0,0) size 285x20
-                RenderText {#text} at (0,0) size 82x19
-                  text run at (0,0) width 82: "overflow:auto"
-              RenderBlock {DIV} at (0,20) size 285x600
-              RenderBlock {DIV} at (0,770) size 285x500
-          layer at (8,83) size 150x150 clip at (8,83) size 135x150 scrollY 478 scrollHeight 866
-            RenderBlock {DIV} at (0,620) size 150x150
-              RenderBlock (anonymous) at (0,0) size 135x20
-                RenderText {#text} at (0,0) size 82x19
-                  text run at (0,0) width 82: "overflow:auto"
-              RenderBlock {DIV} at (0,20) size 135x500
-              RenderBlock (anonymous) at (0,520) size 135x46
-                RenderBR {BR} at (0,0) size 0x19
-                RenderButton {INPUT} at (2,22) size 54x22 [bgcolor=#C0C0C0] [border: (2px outset #C0C0C0)]
-                  RenderBlock (anonymous) at (8,3) size 38x16
-                    RenderText {#text} at (0,0) size 38x16
-                      text run at (0,0) width 38: "Button"
-                RenderText {#text} at (0,0) size 0x0
-              RenderBlock {DIV} at (0,566) size 135x300
         RenderText {#text} at (0,0) size 0x0
       RenderBlock {DIV} at (0,674) size 769x500
+layer at (8,528) 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 545 scrollHeight 1270
+      RenderBlock {DIV} at (0,0) size 300x300
+        RenderBlock (anonymous) at (0,0) size 285x20
+          RenderText {#text} at (0,0) size 82x19
+            text run at (0,0) width 82: "overflow:auto"
+        RenderBlock {DIV} at (0,20) size 285x600
+        RenderBlock {DIV} at (0,770) size 285x500
+    layer at (8,83) size 150x150 clip at (8,83) size 135x150 scrollY 478 scrollHeight 866
+      RenderBlock {DIV} at (0,620) size 150x150
+        RenderBlock (anonymous) at (0,0) size 135x20
+          RenderText {#text} at (0,0) size 82x19
+            text run at (0,0) width 82: "overflow:auto"
+        RenderBlock {DIV} at (0,20) size 135x500
+        RenderBlock (anonymous) at (0,520) size 135x46
+          RenderBR {BR} at (0,0) size 0x19
+          RenderButton {INPUT} at (2,22) size 54x22 [bgcolor=#C0C0C0] [border: (2px outset #C0C0C0)]
+            RenderBlock (anonymous) at (8,3) size 38x16
+              RenderText {#text} at (0,0) size 38x16
+                text run at (0,0) width 38: "Button"
+          RenderText {#text} at (0,0) size 0x0
+        RenderBlock {DIV} at (0,566) size 135x300
 scrolled to 0,8
 frame 'fr' scrolled to 0,91