Add type checks to directory listing.

tests/standalone/src/DirectoryInvalidArgumentsTest.dart

+class DirectoryInvalidArgumentsTest {
+  static void testFailingList(Directory d, var recursive) {
+    int errors = 0;
+    d.setErrorHandler((error) {
+      errors += 1;
+    });
+    d.setDoneHandler((completed) {
+      Expect.equals(1, errors);
+      Expect.isFalse(completed);
+    });
+    Expect.equals(0, errors);
+    d.list(recursive);
+  }
+
+  static void testInvalidArguments() {
+    Directory d = new Directory(12);
+    Expect.isFalse(d.exists());
+    try {
+      d.delete();
+      Expect.fail("No exception thrown");
+    } catch (var e) {
+      Expect.isTrue(e is DirectoryException);
+    }
+    try {
+      d.create();
+      Expect.fail("No exception thrown");
+    } catch (var e) {
+      Expect.isTrue(e is DirectoryException);
+    }
+    testFailingList(d, false);
+    d = new Directory(".");
+    testFailingList(d, 1);
+  }
+
+  static void testMain() {
+    testInvalidArguments();
+  }
+}
+
+main() {
+  DirectoryInvalidArgumentsTest.testMain();
+}