Avoid requiring a recalc to update compositing state for iframes

LayoutTests/platform/mac/fast/css/line-height-overflow-expected.txt

Index: LayoutTests/platform/mac/fast/css/line-height-overflow-expected.txt
diff --git a/LayoutTests/fast/css/line-height-overflow-expected.txt b/LayoutTests/platform/mac/fast/css/line-height-overflow-expected.txt
similarity index 64%
copy from LayoutTests/fast/css/line-height-overflow-expected.txt
copy to LayoutTests/platform/mac/fast/css/line-height-overflow-expected.txt
index 87e5e5ceb26648218eb8b4935dc015fa4ef9f28a..f86b0828038c11d450da4263012f862e14401740 100644
--- a/LayoutTests/fast/css/line-height-overflow-expected.txt
+++ b/LayoutTests/platform/mac/fast/css/line-height-overflow-expected.txt
@@ -8,10 +8,11 @@ layer at (0,0) size 785x32802
           text run at (0,0) width 559: "You should see a large green block below that is 32,768px tall. No red should be visible."
         RenderBR {BR} at (559,14) size 0x0
       RenderBlock {DIV} at (0,18) size 769x32768 [bgcolor=#FF0000]
-        RenderPartObject {IFRAME} at (0,0) size 769x32768 [bgcolor=#008000]
-          layer at (0,0) size 769x32768
-            RenderView at (0,0) size 769x32768
-          layer at (0,0) size 769x32768
-            RenderBlock {HTML} at (0,0) size 769x32768
-              RenderBody {BODY} at (8,8) size 753x32752
         RenderText {#text} at (0,0) size 0x0
+layer at (8,26) size 769x32768
+  RenderPartObject {IFRAME} at (0,0) size 769x32768 [bgcolor=#008000]
+    layer at (0,0) size 769x32768
+      RenderView at (0,0) size 769x32768
+    layer at (0,0) size 769x32768
+      RenderBlock {HTML} at (0,0) size 769x32768
+        RenderBody {BODY} at (8,8) size 753x32752