Don't apply clips to children of composited-scrolling elements for overlap testing.

third_party/WebKit/LayoutTests/compositing/overflow/composited-scroll-overlap-test-expected.txt

-scroll me
 {
   "layers": [
     {
       "name": "LayoutView #document",
-      "bounds": [800, 600],
+      "bounds": [785, 721],
       "contentsOpaque": true,
       "drawsContent": true
     },
     {
+      "name": "LayoutBlockFlow DIV id='scroller'",
+      "position": [8, 8],
+      "bounds": [400, 400],
+      "shouldFlattenTransform": false,
+      "drawsContent": true
+    },
+    {
+      "name": "Scrolling Layer",
+      "bounds": [400, 400],
+      "shouldFlattenTransform": false
+    },
+    {
+      "name": "Scrolling Contents Layer",
+      "bounds": [400, 600],
+      "drawsContent": true
+    },
+    {
       "name": "Squashing Containment Layer",
       "shouldFlattenTransform": false
     },
     {
-      "name": "LayoutBlockFlow DIV id='composited'",
-      "position": [8, 8],
-      "bounds": [20, 20]
+      "name": "LayoutBlockFlow DIV id='overlap'",
+      "position": [0, 400],
+      "bounds": [100, 100],
+      "contentsOpaque": true,
+      "drawsContent": true,
+      "backfaceVisibility": "hidden",
+      "backgroundColor": "#FF0000"
     },
     {
-      "name": "Squashing Layer (first squashed layer: LayoutBlockFlow (positioned) DIV id='overlay')",
-      "position": [10, 8],
-      "bounds": [400, 204],
-      "drawsContent": true
-    },
-    {
-      "name": "LayoutBlockFlow DIV id='scroller'",
-      "position": [202, 10],
-      "bounds": [200, 200],
-      "shouldFlattenTransform": false,
-      "drawsContent": true,
-      "backgroundColor": "#FFFF00"
-    },
-    {
-      "name": "Scrolling Layer",
-      "bounds": [185, 200],
-      "shouldFlattenTransform": false
-    },
-    {
-      "name": "Scrolling Contents Layer",
-      "bounds": [185, 400],
-      "contentsOpaque": true,
+      "name": "Squashing Layer (first squashed layer: LayoutBlockFlow (relative positioned) DIV id='target')",
+      "position": [50, 450],
+      "bounds": [100, 100],
       "drawsContent": true
     },
     {
       "name": "Overflow Controls Host Layer",
-      "bounds": [200, 200]
+      "bounds": [400, 400]
     },
     {
       "name": "Vertical Scrollbar Layer",
-      "position": [185, 0],
-      "bounds": [15, 200]
+      "position": [400, 0],
+      "bounds": [0, 400],
+      "drawsContent": true
     }
   ]
 }