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_lineno.py

@@ -0,0 +1,38 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    # Check that error messages put the '^' in the right place.
+
+    threw = False
+    input = """\
+// This is a comment.
+interface Foo {
+};
+
+/* This is also a comment. */
+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.ok(
+            lines[0].endswith("line 6:10"),
+            'First line of error should end with "line 6:10", but was "%s".' % lines[0],
+        )
+        harness.check(
+            lines[1],
+            "interface ?",
+            "Second line of error message is the line which caused the error.",
+        )
+        harness.check(
+            lines[2],
+            " " * (len("interface ?") - 1) + "^",
+            "Correct column pointer in error message.",
+        )
+
+    harness.ok(threw, "Should have thrown.")