Add NoSourceLocationMarker in old source-info engine.

pkg/compiler/lib/src/io/position_information.dart

Index: pkg/compiler/lib/src/io/position_information.dart
diff --git a/pkg/compiler/lib/src/io/position_information.dart b/pkg/compiler/lib/src/io/position_information.dart
index 2f67aa35e89bff1b8a122e1407a4423806d0119e..b1d58e639cd325859db009566625d071ba4aa954 100644
--- a/pkg/compiler/lib/src/io/position_information.dart
+++ b/pkg/compiler/lib/src/io/position_information.dart
@@ -425,7 +425,7 @@ enum CodePositionKind {
 
 /// Processor that associates [SourceLocation]s from [SourceInformation] on
 /// [js.Node]s with the target offsets in a [SourceMapper].
-class PositionSourceInformationProcessor implements SourceInformationProcessor {
+class PositionSourceInformationProcessor extends SourceInformationProcessor {
   final CodePositionRecorder codePositionRecorder = new CodePositionRecorder();
   CodePositionMap codePositionMap;
   List<TraceListener> traceListeners;