Explicitly generate ComputedStyleBase subgroup copy constructors.

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

Index: third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl
diff --git a/third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl b/third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl
index 56d3f9db36dc79e88c04503199e9e0cd1cea6d1a..956b9747f5a3f55a015812f9512799ba6ef8df46 100644
--- a/third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl
+++ b/third_party/WebKit/Source/build/scripts/templates/fields/group.tmpl
@@ -1,7 +1,7 @@
 {% from 'fields/field.tmpl' import encode, declare_storage, compare %}
 {% from 'macros.tmpl' import print_if %}
 {% macro define_field_group_class(group): -%}
-class {{group.type_name}} : public RefCountedCopyable<{{group.type_name}}> {
+class {{group.type_name}} : public RefCounted<{{group.type_name}}> {
  public:
   static PassRefPtr<{{group.type_name}}> Create() {
     return AdoptRef(new {{group.type_name}});
@@ -30,6 +30,10 @@ class {{group.type_name}} : public RefCountedCopyable<{{group.type_name}}> {
   {% endfor %}
   {}
 
-  {{group.type_name}}(const {{group.type_name}}&) = default;
+  {{group.type_name}}(const {{group.type_name}}& other) :
+  {% for field in group.fields %}
+      {{field.name}}(other.{{field.name}}){{print_if(not loop.last, ',')}}
+  {% endfor %}
+  {}
 };
 {%- endmacro %}