Expose remaining 'errors' in an unified dart:core.

lib/compiler/implementation/lib/errors.dart

Index: lib/compiler/implementation/lib/errors.dart
diff --git a/lib/compiler/implementation/lib/errors.dart b/lib/compiler/implementation/lib/errors.dart
new file mode 100644
index 0000000000000000000000000000000000000000..319abc9e6538df5d40ae58d057ddbd7bc3704d05
--- /dev/null
+++ b/lib/compiler/implementation/lib/errors.dart
@@ -0,0 +1,29 @@
+// Copyright (c) 2012, 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.
+
+class TypeErrorImplementation implements TypeError {
+  final String msg;
+  const TypeErrorImplementation(String this.msg);
+  String toString() => msg;
+}
+
+/** Thrown by the 'as' operator if the cast isn't valid. */
+class CastExceptionImplementation implements CastException {
+  // TODO(lrn): Change actualType and expectedType to "Type" when reified
+  // types are available.
+  final Object actualType;
+  final Object expectedType;
+
+  CastExceptionImplementation(this.actualType, this.expectedType);
+
+  String toString() {
+    return "CastException: Casting value of type $actualType to"
+           " incompatible type $expectedType";
+  }
+}
+
+class FallThroughErrorImplementation implements FallThroughError {
+  const FallThroughErrorImplementation();
+  String toString() => "Switch case fall-through.";
+}