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_empty_enum.py

@@ -0,0 +1,17 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            enum TestEmptyEnum {
+            };
+        """
+        )
+
+        harness.ok(False, "Should have thrown!")
+    except:
+        harness.ok(True, "Parsing TestEmptyEnum enum should fail")
+
+    results = parser.finish()