Always composite position: fixed elements with composited descendants.

third_party/WebKit/LayoutTests/compositing/always-composite-fixed-position-when-descendants-composite-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "position": [8, 8],
-          "bounds": [200, 10],
-          "children": [
-            {
-              "bounds": [200, 10],
-              "contentsOpaque": true,
-              "drawsContent": true,
-              "backgroundColor": "#F5F5F5"
-            }
-          ]
-        },
-        {
-          "position": [8, 0],
           "bounds": [100, 100],
           "contentsOpaque": true,
           "drawsContent": true,
-          "backgroundColor": "#90EE90"
+          "backgroundColor": "#D3D3D3",
+          "children": [
+            {
+              "position": [50, 50],
+              "bounds": [50, 50],
+              "contentsOpaque": true,
+              "drawsContent": true,
+              "backgroundColor": "#ADD8E6"
+            }
+          ]
         }
       ]
     }
   ]
 }