Add keyword_subset field template and generate text-decoration-line.

third_party/WebKit/Source/build/scripts/templates/ComputedStyleBaseConstants.h.tmpl

-{% from 'macros.tmpl' import license %}
+{% from 'macros.tmpl' import license, print_if %}
 {{license()}}
 
 #ifndef ComputedStyleBaseConstants_h
 #define ComputedStyleBaseConstants_h
 
 namespace blink {
 
 // TODO(sashab): Move these enums to their own namespace, or add a CSS prefix,
 // for consistency and to prevent name conflicts.
 
-{% for enum_name, enum_values in enums.items() %}
-enum class {{enum_name}} : unsigned {
-  {% for enum_value in enum_values %}
-  {{enum_value}},
+{% for enum in enums %}
+enum class {{enum.type_name}} : unsigned {
+  {% for value in enum.values %}
+  {{value}}{{print_if(enum.is_set, " = " ~ (0 if loop.first else 2**loop.index0))}},
   {% endfor %}
 };
 
+{% if enum.is_set %}
+static const int k{{enum.type_name}}Bits = {{enum.values|length - 1}};
+
+{% for op in ('|', '^') %}
+inline {{enum.type_name}} operator{{op}}({{enum.type_name}} a, {{enum.type_name}} b) {
+  return static_cast<{{enum.type_name}}>(
+    static_cast<unsigned>(a) {{op}} static_cast<unsigned>(b)
+  );
+}
+inline {{enum.type_name}}& operator{{op}}=({{enum.type_name}}& a, {{enum.type_name}} b) {
+  return a = a {{op}} b;
+}
+
+{% endfor %}
+{% endif %}
 {% endfor %}
 } // namespace blink
 
 #endif // ComputedStyleBaseConstants_h