Check if value changed when setting nested fields in ComputedStyleBase.

third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl

Index: third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl
diff --git a/third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl b/third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl
index f029a40e5c487708e30fb14dce93c5d416ef31a6..11474ec1496479ba07715453fc022b31dc19298a 100644
--- a/third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl
+++ b/third_party/WebKit/Source/build/scripts/templates/fields/field.tmpl
@@ -30,6 +30,15 @@ static_cast<{{field.type_name}}>({{value}})
 {%- endif %}
 {% endmacro %}
 
+{% macro set_if_changed(field, value) %}
+{% if field.group_member_name -%}
+if (!({{getter_expression(field)}} == {{value}}))
+  {{setter_expression(field)}} = {{value}};
+{%- else -%}
+{{field.name}} = {{value}};
+{%- endif %}
+{% endmacro %}
+
 {% macro nonconst_ref(field) %}
 {% if field.is_bit_field -%}
 {{field.type_name}}
@@ -99,4 +108,4 @@ if ({{subgroup.member_name}}.Get() != other.{{subgroup.member_name}}.Get()) {
 if ({{getter_expression(field)}} != other.{{getter_expression(field)}})
   return true;
 {% endfor %}
-{% endmacro %}
+{% endmacro %}