Add LineScanner and SpanScanner classes to string_scanner.

pkg/string_scanner/test/span_scanner_test.dart

Index: pkg/string_scanner/test/span_scanner_test.dart
diff --git a/pkg/string_scanner/test/span_scanner_test.dart b/pkg/string_scanner/test/span_scanner_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..93ba0b659e6d9d0a5d146bb00abe0334de306a14
--- /dev/null
+++ b/pkg/string_scanner/test/span_scanner_test.dart
@@ -0,0 +1,60 @@
+// 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 string_scanner.span_scanner_test;
+
+import 'package:string_scanner/string_scanner.dart';
+import 'package:unittest/unittest.dart';
+
+void main() {
+  var scanner;
+  setUp(() {
+    scanner = new SpanScanner('foo\nbar\nbaz', 'source');
+  });
+
+  test("tracks the span for the last match", () {
+    scanner.scan('fo');
+    scanner.scan('o\nba');
+
+    var span = scanner.lastSpan;
+    expect(span.start.offset, equals(2));
+    expect(span.start.line, equals(0));
+    expect(span.start.column, equals(2));
+    expect(span.start.sourceUrl, equals('source'));
+
+    expect(span.end.offset, equals(6));
+    expect(span.end.line, equals(1));
+    expect(span.end.column, equals(2));
+    expect(span.start.sourceUrl, equals('source'));
+
+    expect(span.text, equals('o\nba'));
+  });
+
+  test(".spanFrom() returns a span from a previous state", () {
+    scanner.scan('fo');
+    var state = scanner.state;
+    scanner.scan('o\nba');
+    scanner.scan('r\nba');
+
+    var span = scanner.spanFrom(state);
+    expect(span.text, equals('o\nbar\nba'));
+  });
+
+  test(".emptySpan returns an empty span at the current location", () {
+    scanner.scan('foo\nba');
+
+    var span = scanner.emptySpan;
+    expect(span.start.offset, equals(6));
+    expect(span.start.line, equals(1));
+    expect(span.start.column, equals(2));
+    expect(span.start.sourceUrl, equals('source'));
+
+    expect(span.end.offset, equals(6));
+    expect(span.end.line, equals(1));
+    expect(span.end.column, equals(2));
+    expect(span.start.sourceUrl, equals('source'));
+
+    expect(span.text, equals(''));
+  });
+}