[Fasta] Include line starts

pkg/front_end/lib/src/fasta/kernel/kernel_target.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.
 
 library fasta.kernel_target;
 
 import 'dart:async' show Future;
 
 import 'dart:io' show File, IOSink;
 
@@ skipping 292 matching lines @@
       mainBuilder.body = new ExpressionStatement(
           new Throw(new StringLiteral("${errors.join('\n')}")));
     }
     library.build();
     return link(<Library>[library.library]);
   }
 
   /// Creates a program by combining [libraries] with the libraries of
   /// `dillTarget.loader.program`.
   Program link(List<Library> libraries) {
-    Map<String, Source> uriToSource = <String, Source>{};
-
-    // for (Library library in libraries) {
-    //   // TODO(ahe): Compute line starts instead.
-    //   uriToLineStarts[library.fileUri] = <int>[0];
-    // }
+    Map<String, Source> uriToSource =
+        new Map<String, Source>.from(this.uriToSource);
 
     final Program binary = dillTarget.loader.program;
     if (binary != null) {
       libraries.addAll(binary.libraries);
       uriToSource.addAll(binary.uriToSource);
     }
 
     // TODO(ahe): Remove this line. Kernel seems to generate a default line map
     // that used when there's no fileUri on an element. Instead, ensure all
     // elements have a fileUri.
@@ skipping 280 matching lines @@
   }
   for (Constructor constructor in superclass.constructors) {
     if (constructor.name.name.isEmpty) {
       return constructor.function.requiredParameterCount == 0
           ? constructor
           : null;
     }
   }
   return null;
 }