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_error_colno.py

@@ -0,0 +1,24 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    # Check that error messages put the '^' in the right place.
+
+    threw = False
+    input = "interface ?"
+    try:
+        parser.parse(input)
+        results = parser.finish()
+    except WebIDL.WebIDLError as e:
+        threw = True
+        lines = str(e).split("\n")
+
+        harness.check(len(lines), 3, "Expected number of lines in error message")
+        harness.check(lines[1], input, "Second line shows error")
+        harness.check(
+            lines[2],
+            " " * (len(input) - 1) + "^",
+            "Correct column pointer in error message",
+        )
+
+    harness.ok(threw, "Should have thrown.")