Use generated copy and compare for VerticalAlign in ComputedStyle.

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

 {
 // This file specifies fields in ComputedStyle that we would like to
 // generate, but are not CSS properties.
 
   parameters: {
     // - field_size
     // Number of bits needed to store this field. Only used for storage_only
     // fields. If specified, the field will be stored as bit field. Otherwise
     // it will be stored as a normal data member.
     field_size: {
@@ skipping 135 matching lines @@
     {
       name: "HasSimpleUnderline",
       field_template: "storage_only",
       field_size: 1,
       default_value: "false",
       type_name: "bool",
       inherited: true,
       has_custom_compare_and_copy: true,
     },
     // TODO(shend): vertical align is actually a CSS property, but since we don't support union fields
-    // which can be either a keyword or Length, this is generated as a nonproperty for now. Remove this
-    // once we can support union fields and groups.
+    // which can be either a keyword or Length, this is specified in this file for now. Remove this
+    // once we can support union fields.
     {
       name: "VerticalAlign",
       field_template: "storage_only",
       field_size: 4,
       default_value: "EVerticalAlign::kBaseline",
       type_name: "EVerticalAlign",
-      has_custom_compare_and_copy: true,
     },
     {
       name: "border",
       field_template: "storage_only",
       field_type_path: "core/style/BorderData",
       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",
     },
   ],
 }