Generate subgroup StyleSurroundData in ComputedStyle.

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

Index: third_party/WebKit/Source/core/css/CSSProperties.json5
diff --git a/third_party/WebKit/Source/core/css/CSSProperties.json5 b/third_party/WebKit/Source/core/css/CSSProperties.json5
index eccec5441e4e39a870d8440f0bff60e9bd0e457b..60ad59fcf3c419d7175e3101b2243b56f6a2f708 100644
--- a/third_party/WebKit/Source/core/css/CSSProperties.json5
+++ b/third_party/WebKit/Source/core/css/CSSProperties.json5
@@ -61,6 +61,14 @@
       valid_values: ["parseSingleValue", "parseShorthand"],
     },
 
+    // - field_group
+    // Name of the group that this field belongs to. Fields in the same group are stored
+    // together as a nested class inside ComputedStyle and dynamically allocated on use.
+    // Leave this out if the field is stored directly on ComputedStyle.
+    field_group: {
+      value_type: "str"
+    },
+
     // - field_template
     // Affects how the interface to this field is generated.
     // TODO(sashab, meade): Remove this once TypedOM types are specified for
@@ -796,6 +804,10 @@
       keywords: ["auto"],
       supports_percentage: true,
       typedom_types: ["Length"],
+      field_template: "external",
+      field_type_path: "platform/Length",
+      field_group: "surround",
+      default_value: "Length()",
     },
     {
       name: "box-shadow",
@@ -1198,6 +1210,10 @@
       keywords: ["auto"],
       supports_percentage: true,
       typedom_types: ["Length"],
+      field_template: "external",
+      field_type_path: "platform/Length",
+      field_group: "surround",
+      default_value: "Length()",
     },
     {
       name: "letter-spacing",
@@ -1597,6 +1613,10 @@
       keywords: ["auto"],
       supports_percentage: true,
       typedom_types: ["Length"],
+      field_template: "external",
+      field_type_path: "platform/Length",
+      field_group: "surround",
+      default_value: "Length()",
     },
     {
       name: "r",
@@ -1915,6 +1935,10 @@
       keywords: ["auto"],
       supports_percentage: true,
       typedom_types: ["Length"],
+      field_template: "external",
+      field_type_path: "platform/Length",
+      field_group: "surround",
+      default_value: "Length()",
     },
     {
       name: "touch-action",