Move scanner tests into the front_end package.

pkg/front_end/lib/src/scanner/reader.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.
 
 /**
  * An object used by the scanner to read the characters to be scanned.
  */
 abstract class CharacterReader {
   /**
    * The current offset relative to the beginning of the source. Return the
@@ skipping 24 matching lines @@
    * location to be excluded if the offset is negative.
    */
   String getString(int start, int endDelta);
 
   /**
    * Return the character at the current position without changing the current
    * position.
    */
   int peek();
 }
+
+/**
+ * A [CharacterReader] that reads characters from a character sequence.
+ */
+class CharSequenceReader implements CharacterReader {
+  /**
+   * The sequence from which characters will be read.
+   */
+  final String _sequence;
+
+  /**
+   * The number of characters in the string.
+   */
+  int _stringLength;
+
+  /**
+   * The index, relative to the string, of the next character to be read.
+   */
+  int _charOffset;
+
+  /**
+   * Initialize a newly created reader to read the characters in the given
+   * [_sequence].
+   */
+  CharSequenceReader(this._sequence) {
+    this._stringLength = _sequence.length;
+    this._charOffset = 0;
+  }
+
+  @override
+  int get offset => _charOffset - 1;
+
+  @override
+  void set offset(int offset) {
+    _charOffset = offset + 1;
+  }
+
+  @override
+  int advance() {
+    if (_charOffset >= _stringLength) {
+      return -1;
+    }
+    return _sequence.codeUnitAt(_charOffset++);
+  }
+
+  @override
+  String getString(int start, int endDelta) =>
+      _sequence.substring(start, _charOffset + endDelta);
+
+  @override
+  int peek() {
+    if (_charOffset >= _stringLength) {
+      return -1;
+    }
+    return _sequence.codeUnitAt(_charOffset);
+  }
+}
+
+/**
+ * A [CharacterReader] that reads characters from a character sequence, but adds
+ * a delta when reporting the current character offset so that the character
+ * sequence can be a subsequence from a larger sequence.
+ */
+class SubSequenceReader extends CharSequenceReader {
+  /**
+   * The offset from the beginning of the file to the beginning of the source
+   * being scanned.
+   */
+  final int _offsetDelta;
+
+  /**
+   * Initialize a newly created reader to read the characters in the given
+   * [sequence]. The [_offsetDelta] is the offset from the beginning of the file
+   * to the beginning of the source being scanned
+   */
+  SubSequenceReader(String sequence, this._offsetDelta) : super(sequence);
+
+  @override
+  int get offset => _offsetDelta + super.offset;
+
+  @override
+  void set offset(int offset) {
+    super.offset = offset - _offsetDelta;
+  }
+
+  @override
+  String getString(int start, int endDelta) =>
+      super.getString(start - _offsetDelta, endDelta);
+}