Add back a utility method needed by tests

pkg/analyzer/lib/src/generated/source.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 engine.source;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/file_system/file_system.dart';
@@ skipping 190 matching lines @@
    * @param lineStarts the offsets of the first character of each line in the source code
    */
   LineInfo(this._lineStarts) {
     if (_lineStarts == null) {
       throw new IllegalArgumentException("lineStarts must be non-null");
     } else if (_lineStarts.length < 1) {
       throw new IllegalArgumentException("lineStarts must be non-empty");
     }
   }
 
-//  /**
-//   * Return the offset of the first character on the line with the given
-//   * [lineNumber].
-//   */
-//  int getLineOffset(int lineNumber) {
-//    if (lineNumber < 0 || lineNumber >= _lineStarts.length) {
-//      throw new ArgumentError('Invalid line number: $lineNumber');
-//    }
-//    return _lineStarts[lineNumber];
-//  }
-
   /**
    * Return the location information for the character at the given offset.
    *
    * @param offset the offset of the character for which location information is to be returned
    * @return the location information for the character at the given offset
    */
   LineInfo_Location getLocation(int offset) {
     var min = 0;
     var max = _lineStarts.length - 1;
 
@@ skipping 19 matching lines @@
         max = midpoint - 1;
       } else {
         min = midpoint;
       }
     }
 
     _previousLine = min;
 
     return new LineInfo_Location(min + 1, offset - _lineStarts[min] + 1);
   }
+
+  /**
+   * Return the offset of the first character on the line with the given
+   * [lineNumber].
+   */
+  int getOffsetOfLine(int lineNumber) {
+    if (lineNumber < 0 || lineNumber >= _lineStarts.length) {
+      throw new ArgumentError('Invalid line number: $lineNumber');
+    }
+    return _lineStarts[lineNumber];
+  }
 }
 
 /**
  * Instances of the class `Location` represent the location of a character as a line and
  * column pair.
  */
 class LineInfo_Location {
   /**
    * The one-based index of the line containing the character.
    */
@@ skipping 817 matching lines @@
   Source resolveAbsolute(Uri uri, [Uri actualUri]);
 
   /**
    * Return an absolute URI that represents the given [source], or `null` if a
    * valid URI cannot be computed.
    *
    * The computation should be based solely on [source.fullName].
    */
   Uri restoreAbsolute(Source source) => null;
 }