Fix squashing to treat perspective and preserve3d elements as transform ancestors.

LayoutTests/compositing/squashing/squashing-inside-perspective-with-reparented-scrolling.html

Index: LayoutTests/compositing/squashing/squashing-inside-perspective-with-reparented-scrolling.html
diff --git a/LayoutTests/compositing/overflow/reparented-unclipped-overlay-scrollbars-with-offset-from-renderer.html b/LayoutTests/compositing/squashing/squashing-inside-perspective-with-reparented-scrolling.html
similarity index 61%
copy from LayoutTests/compositing/overflow/reparented-unclipped-overlay-scrollbars-with-offset-from-renderer.html
copy to LayoutTests/compositing/squashing/squashing-inside-perspective-with-reparented-scrolling.html
index 339be18ace9a3f1308889b685a42ed68ed664fe8..ddeed461d3b6d0fa751bdbf2541234b6e83103b2 100644
--- a/LayoutTests/compositing/overflow/reparented-unclipped-overlay-scrollbars-with-offset-from-renderer.html
+++ b/LayoutTests/compositing/squashing/squashing-inside-perspective-with-reparented-scrolling.html
@@ -27,13 +27,19 @@
     height: 500px;
 }
 </style>
+<div style="z-index: 1; position: absolute"></div>
+<div style="z-index: 0; perspective: 1000px; position: absolute;">
+    <div id='scroller'>
+        <div id='fixed'></div>
+        <div id='scrolled'></div>
+    </div>
+</div>
 <script>
+// Check that a case with a reparented overflow control and a containing perspective node
+// paints the same with and without layer squashing.
 if (window.internals) {
     window.internals.settings.setOverlayScrollbarsEnabled(true);
     window.internals.settings.setPreferCompositingToLCDTextEnabled(true);
+    window.internals.settings.setLayerSquashingEnabled(true);
 }
 </script>
-<div id='scroller'>
-    <div id='fixed'></div>
-    <div id='scrolled'></div>
-</div>