Fixed assert causing crash when attempting to load a library from an invalid path.

tests/language/vm/regress_27201_test.dart

+/*
+ * Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+ * for details. All rights reserved. Use of this source code is governed by a
+ * BSD-style license that can be found in the LICENSE file.
+ */
+import "dart:async";
+import "package:expect/expect.dart";
+import "regress_27201_lib.dart" deferred as p;
+import "regress_27201_bad_lib_path.dart" deferred as q;
+
+test_loaded() {
+  try {
+    p.someFunc();
+  } catch (e) {
+    Expect.fail("Should not be here");
+  }
+  try {
+    p.someGetter;
+  } catch (e) {
+    Expect.fail("Should not be here");
+  }
+  try {
+    p.someSetter = 1;
+  } catch (e) {
+    Expect.fail("Should not be here");
+  }
+  try {
+    p.Func;
+  } catch (e) {
+    Expect.fail("Should not be here");
+  }
+  try {
+    Expect.isTrue(p.loadLibrary() is Future);
+  } catch (e) {
+    Expect.fail("Should not be here");
+  }
+}
+
+
+main() {
+  p.loadLibrary().then((v) {
+    test_loaded();
+  },
+  onError: (e) {
+    Expect.fail("Should have loaded library!");
+  });
+
+  // Ensure bad library import is handled correctly.
+  q.loadLibrary().then((v) {
+    Expect.fail("Should have failed");
+  },
+  onError: (e) {
+    Expect.throws(() => q.x);
+  });
+}
+