Initial API for the Dart front_end package.

pkg/front_end/lib/compilation_error.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.
+
+/// Defines the API for the front end to communicate information about
+/// compilation errors to clients.
+library front_end.compilation_error;
+
+import 'package:source_span/source_span.dart' show SourceSpan;
+
+/// A single error that occurred during compilation, and information about where
+/// it occurred.
+///
+/// TODO(paulberry): add a reference to the analyzer error code.
+///
+/// TODO(paulberry): add a correction message, once most analyzer errors have
+/// one.
+abstract class CompilationError {
+  /// A text description of the compile error.
+  String get message;
+
+  /// The source location where the error occurred.
+  SourceSpan get location;
+}