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_treatNonCallableAsNull.py

@@ -0,0 +1,80 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        [TreatNonCallableAsNull] callback Function = any(any... arguments);
+
+        interface TestTreatNonCallableAsNull1 {
+          attribute Function? onfoo;
+          attribute Function onbar;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    iface = results[1]
+    attr = iface.members[0]
+    harness.check(attr.type.treatNonCallableAsNull(), True, "Got the expected value")
+    attr = iface.members[1]
+    harness.check(attr.type.treatNonCallableAsNull(), False, "Got the expected value")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback Function = any(any... arguments);
+
+            interface TestTreatNonCallableAsNull2 {
+              [TreatNonCallableAsNull] attribute Function onfoo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback Function = any(any... arguments);
+
+            [TreatNonCallableAsNull]
+            interface TestTreatNonCallableAsNull3 {
+               attribute Function onfoo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            [TreatNonCallableAsNull, LegacyTreatNonObjectAsNull]
+            callback Function = any(any... arguments);
+        """
+        )
+
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")