Create a top-level "third_party" directory

This directory now contains third_party software that is vendored into
the Servo source tree. The idea is that it would eventually hold
webrender and other crates from mozilla-central as well with a standard
patch management approach for each.

third_party/WebIDL/tests/test_callback.py

@@ -0,0 +1,42 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestCallback {
+          attribute CallbackType? listener;
+        };
+
+        callback CallbackType = boolean (unsigned long arg);
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestCallback interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestCallback", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestCallback", "Interface has the right name")
+    harness.check(len(iface.members), 1, "Expect %s members" % 1)
+
+    attr = iface.members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.ok(attr.isAttr(), "Should be an attribute")
+    harness.ok(not attr.isMethod(), "Attr is not an method")
+    harness.ok(not attr.isConst(), "Attr is not a const")
+    harness.check(
+        attr.identifier.QName(), "::TestCallback::listener", "Attr has the right QName"
+    )
+    harness.check(attr.identifier.name, "listener", "Attr has the right name")
+    t = attr.type
+    harness.ok(not isinstance(t, WebIDL.IDLWrapperType), "Attr has the right type")
+    harness.ok(isinstance(t, WebIDL.IDLNullableType), "Attr has the right type")
+    harness.ok(t.isCallback(), "Attr has the right type")
+
+    callback = results[1]
+    harness.ok(not callback.isConstructor(), "callback is not constructor")