Revert "Removes dartc reliance on its own libraries, now can be targeted at any implementation's li…

compiler/lib/error.dart

+// Copyright (c) 2011, 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.
+
+// Exceptions thrown by the VM -- user code should never throw these directly.
+// TODO(jat): these should be compatible with the definitions in runtime/lib/error.dart
+
+class AssertionError {
+  const AssertionError();
+
+  String toString() {
+    return "Failed assertion";
+  }
+}
+
+class TypeError extends AssertionError {
+  final String dstType;
+  final String srcType;
+
+  const TypeError(this.srcType, this.dstType);
+
+  String toString() {
+    return "Failed type check: type $srcType is not assignable to type $dstType";
+  }
+}
+
+class FallThroughError {
+  const FallThroughError();
+
+  String toString() {
+    return "Switch case fall-through";
+  }
+}
+