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_callback_interface.py

@@ -0,0 +1,106 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        callback interface TestCallbackInterface {
+          attribute boolean bool;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    iface = results[0]
+
+    harness.ok(iface.isCallback(), "Interface should be a callback")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestInterface {
+            };
+            callback interface TestCallbackInterface : TestInterface {
+              attribute boolean bool;
+            };
+        """
+        )
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Should not allow non-callback parent of callback interface")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestInterface : TestCallbackInterface {
+            };
+            callback interface TestCallbackInterface {
+              attribute boolean bool;
+            };
+        """
+        )
+        results = parser.finish()
+    except:
+        threw = True
+
+    harness.ok(threw, "Should not allow callback parent of non-callback interface")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        callback interface TestCallbackInterface1 {
+          undefined foo();
+        };
+        callback interface TestCallbackInterface2 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+        };
+        callback interface TestCallbackInterface3 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          static undefined bar();
+        };
+        callback interface TestCallbackInterface4 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          static undefined bar();
+          const long baz = 5;
+        };
+        callback interface TestCallbackInterface5 {
+          static attribute boolean bool;
+          undefined foo();
+        };
+        callback interface TestCallbackInterface6 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          undefined bar();
+        };
+        callback interface TestCallbackInterface7 {
+          static attribute boolean bool;
+        };
+        callback interface TestCallbackInterface8 {
+          attribute boolean bool;
+        };
+        callback interface TestCallbackInterface9 : TestCallbackInterface1 {
+          undefined foo();
+        };
+        callback interface TestCallbackInterface10 : TestCallbackInterface1 {
+          undefined bar();
+        };
+    """
+    )
+    results = parser.finish()
+    for (i, iface) in enumerate(results):
+        harness.check(
+            iface.isSingleOperationInterface(),
+            i < 4,
+            "Interface %s should be a single operation interface"
+            % iface.identifier.name,
+        )