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_identifier_conflict.py

@@ -0,0 +1,49 @@
+# Import the WebIDL module, so we can do isinstance checks and whatnot
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            enum Foo { "a" };
+            interface Foo;
+        """
+        )
+        results = parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Name collision" in str(e), "Should have name collision for interface"
+        )
+
+    parser = parser.reset()
+    try:
+        parser.parse(
+            """
+            dictionary Foo { long x; };
+            enum Foo { "a" };
+        """
+        )
+        results = parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Name collision" in str(e), "Should have name collision for dictionary"
+        )
+
+    parser = parser.reset()
+    try:
+        parser.parse(
+            """
+            enum Foo { "a" };
+            enum Foo { "b" };
+        """
+        )
+        results = parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Multiple unresolvable definitions" in str(e),
+            "Should have name collision for dictionary",
+        )