Remove support for the old Span classes from source_maps.

pkg/source_maps/lib/src/source_map_span.dart

+// Copyright (c) 2014, 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.
+
+library source_maps.source_map_span;
+
+import 'package:source_span/source_span.dart';
+
+/// A [SourceSpan] for spans coming from or being written to source maps.
+///
+/// These spans have an extra piece of metadata: whether or not they represent
+/// an identifier (see [isIdentifier]).
+class SourceMapSpan extends SourceSpanBase {
+  /// Whether this span represents an identifier.
+  ///
+  /// If this is `true`, [text] is the value of the identifier.
+  final bool isIdentifier;
+
+  SourceMapSpan(SourceLocation start, SourceLocation end, String text,
+          {this.isIdentifier: false})
+      : super(start, end, text);
+
+  /// Creates a [SourceMapSpan] for an identifier with value [text] starting at
+  /// [start].
+  ///
+  /// The [end] location is determined by adding [text] to [start].
+  SourceMapSpan.identifier(SourceLocation start, String text)
+      : this(
+          start,
+          new SourceLocation(start.offset + text.length,
+              sourceUrl: start.sourceUrl,
+              line: start.line,
+              column: start.column + text.length),
+          text,
+          isIdentifier: true);
+}
+
+/// A wrapper aruond a [FileSpan] that implements [SourceMapSpan].
+class SourceMapFileSpan implements SourceMapSpan, FileSpan {
+  final FileSpan _inner;
+  final bool isIdentifier;
+
+  SourceFile get file => _inner.file;
+  FileLocation get start => _inner.start;
+  FileLocation get end => _inner.end;
+  String get text => _inner.text;
+  Uri get sourceUrl => _inner.sourceUrl;
+  int get length => _inner.length;
+
+  SourceMapFileSpan(this._inner, {this.isIdentifier: false});
+
+  int compareTo(SourceSpan other) => _inner.compareTo(other);
+  SourceSpan union(SourceSpan other) => _inner.union(other);
+  FileSpan expand(FileSpan other) => _inner.expand(other);
+  String message(String message, {color}) =>
+      _inner.message(message, color: color);
+  String toString() => _inner.toString()
+      .replaceAll("FileSpan", "SourceMapFileSpan");
+}