Initial scroll-blocks-on compositor integration

LayoutTests/compositing/layer-creation/scroll-blocks-on-default-expected.txt

Index: LayoutTests/compositing/layer-creation/scroll-blocks-on-default-expected.txt
diff --git a/LayoutTests/compositing/layer-creation/scroll-blocks-on-default-expected.txt b/LayoutTests/compositing/layer-creation/scroll-blocks-on-default-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..8e095b68467ce54ad06315a7d6f3bd21bdd4d81e
--- /dev/null
+++ b/LayoutTests/compositing/layer-creation/scroll-blocks-on-default-expected.txt
@@ -0,0 +1,20 @@
+Verify we get the default scroll-blocks-on mode applied to the viewport, no additional layers created (even with an iframe), and no scroll-blocks-on mode applied to any other layer.
+
+{
+  "bounds": [800, 600],
+  "children": [
+    {
+      "bounds": [800, 600],
+      "scrollBlocksOn": ["StartTouch", "WheelEvent"],
+      "contentsOpaque": true,
+      "drawsContent": true,
+      "children": [
+        {
+          "position": [8, 48],
+          "bounds": [20, 20]
+        }
+      ]
+    }
+  ]
+}
+