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_unenumerable_own_properties.py

@@ -0,0 +1,71 @@
+def WebIDLTest(parser, harness):
+
+    parser.parse(
+        """
+        interface Foo {};
+        [LegacyUnenumerableNamedProperties]
+        interface Bar : Foo {
+          getter long(DOMString name);
+        };
+        interface Baz : Bar {
+          getter long(DOMString name);
+        };
+        """
+    )
+    results = parser.finish()
+    harness.check(len(results), 3, "Should have three interfaces")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties]
+            interface NoNamedGetter {
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception as x:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties=Foo]
+            interface ShouldNotHaveArg {
+              getter long(DOMString name);
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception as x:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties]
+            interface Foo {
+              getter long(DOMString name);
+            };
+            interface Bar : Foo {};
+            [LegacyUnenumerableNamedProperties]
+            interface Baz : Bar {
+              getter long(DOMString name);
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception as x:
+        threw = True
+    harness.ok(threw, "Should have thrown.")