Count partial mixins as deps

resources/idlharness.js

@@ -305,7 +305,17 @@ IdlArray.prototype.add_dependency_idls = function(raw_idls, options)
                 if (parsed[dep_type]) {
                     const inheriting = parsed[dep_type];
                     const inheritor = parsed.name || parsed.target;
-                    for (const dep of [inheriting, inheritor]) {
+                    const deps = [inheriting];
+                    // For A includes B, we can ignore A, unless B (or some of its
+                    // members) is being tested.
+                    if (dep_type !== "includes"
+                        || inheriting in this.members && !this.members[inheriting].untested
+                        || this.partials.find(function(p) {
+                                return p.name === inheriting;
+                            })) {
+                        deps.push(inheritor);
+                    }
+                    for (const dep of deps) {
                         new_options.only.push(dep);
                         all_deps.add(dep);
                         follow_up.add(dep);