Add LineScanner and SpanScanner classes to string_scanner.

pkg/string_scanner/test/string_scanner_test.dart

Index: pkg/string_scanner/test/string_scanner_test.dart
diff --git a/pkg/string_scanner/test/string_scanner_test.dart b/pkg/string_scanner/test/string_scanner_test.dart
index 0cab6273ebf2e2975bf374b26b7f14574abd76f2..6144bf9c007c3dcc30b09684d9899df46c8ddf68 100644
--- a/pkg/string_scanner/test/string_scanner_test.dart
+++ b/pkg/string_scanner/test/string_scanner_test.dart
@@ -31,6 +31,18 @@ void main() {
       expect(scanner.position, equals(0));
     });
 
+    test("readChar fails and doesn't change the state", () {
+      expect(scanner.readChar, throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("peekChar returns null and doesn't change the state", () {
+      expect(scanner.peekChar(), isNull);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
     test("scan returns false and doesn't change the state", () {
       expect(scanner.scan(new RegExp('.')), isFalse);
       expect(scanner.lastMatch, isNull);
@@ -85,6 +97,24 @@ void main() {
       expect(scanner.position, equals(0));
     });
 
+    test('readChar returns the first character and moves forward', () {
+      expect(scanner.readChar(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(1));
+    });
+
+    test('peekChar returns the first character', () {
+      expect(scanner.peekChar(), equals(0x66));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('peekChar with an argument returns the nth character', () {
+      expect(scanner.peekChar(4), equals(0x62));
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
     test("a matching scan returns true and changes the state", () {
       expect(scanner.scan(new RegExp('f(..)')), isTrue);
       expect(scanner.lastMatch[1], equals('oo'));
@@ -200,6 +230,18 @@ void main() {
       expect(scanner.position, equals(7));
     });
 
+    test("readChar fails and doesn't change the state", () {
+      expect(scanner.readChar, throwsFormatException);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("peekChar returns null and doesn't change the state", () {
+      expect(scanner.peekChar(), isNull);
+      expect(scanner.lastMatch, isNotNull);
+      expect(scanner.position, equals(7));
+    });
+
     test("scan returns false and sets lastMatch to null", () {
       expect(scanner.scan(new RegExp('.')), isFalse);
       expect(scanner.lastMatch, isNull);