Generate StyleBackgroundData in ComputedStyleBase.

third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5

Index: third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5
diff --git a/third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5 b/third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5
index e0288d6618ec3128cdbbe1f58872bf34852cfd52..68e408ab850c5e71eee2c9f48d15d5d91d259541 100644
--- a/third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5
+++ b/third_party/WebKit/Source/core/css/ComputedStyleExtraFields.json5
@@ -169,5 +169,19 @@
       field_group: "surround",
       default_value: "BorderData()",
     },
+    {
+      name: "Background",
+      field_template: "storage_only",
+      field_type_path: "core/style/FillLayer",
+      default_value: "FillLayer(kBackgroundFillLayer, true)",
+      field_group: "background",
+    },
+    {
+      name: "BackgroundColor",
+      field_template: "storage_only",
+      field_type_path: "core/css/StyleColor",
+      default_value: "Color::kTransparent",
+      field_group: "background",
+    },
   ],
 }