Enable compositing of scrolling content on low-DPI when LCD text will be maintained

third_party/WebKit/LayoutTests/compositing/layer-creation/scroll-partial-update-expected.txt

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 {
   "name": "Content Root Layer",
   "bounds": [800, 600],
   "children": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "children": [
         {
           "name": "Squashing Containment Layer",
           "shouldFlattenTransform": false,
           "children": [
             {
               "name": "LayoutBlockFlow DIV id='composited'",
               "position": [8, 8],
               "bounds": [20, 20]
             },
             {
               "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",
+          "children": [
+            {
+              "name": "Scrolling Layer",
+              "bounds": [185, 200],
+              "shouldFlattenTransform": false,
+              "children": [
+                {
+                  "name": "Scrolling Contents Layer",
+                  "bounds": [185, 400],
+                  "contentsOpaque": true,
+                  "drawsContent": true
+                }
+              ]
+            },
+            {
+              "name": "Overflow Controls Host Layer",
+              "bounds": [200, 200],
+              "children": [
+                {
+                  "name": "Vertical Scrollbar Layer",
+                  "position": [185, 0],
+                  "bounds": [15, 200]
+                }
+              ]
+            }
+          ]
         }
       ]
     }
   ]
 }