Add back a utility method needed by tests

pkg/analyzer/lib/src/generated/source.dart

Index: pkg/analyzer/lib/src/generated/source.dart
diff --git a/pkg/analyzer/lib/src/generated/source.dart b/pkg/analyzer/lib/src/generated/source.dart
index 24fec623ea748adab62aba90c34383d566fd6c2a..79cd48f37bcc63620413f00a8c0a2e4ae3ded7ae 100644
--- a/pkg/analyzer/lib/src/generated/source.dart
+++ b/pkg/analyzer/lib/src/generated/source.dart
@@ -208,17 +208,6 @@ class LineInfo {
     }
   }
 
-//  /**
-//   * 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.
    *
@@ -258,6 +247,17 @@ class LineInfo {
 
     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];
+  }
 }
 
 /**