Add a generated ComputedStyleBase class that ComputedStyle extends

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

+{% from 'macros.tmpl' import license %}
+{{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}},
+    {% endfor %}
+};
+
+{% endfor %}
+} // namespace blink
+
+#endif // ComputedStyleBaseConstants_h