Add NoSourceLocationMarker in old source-info engine.

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

Index: pkg/compiler/lib/src/io/start_end_information.dart
diff --git a/pkg/compiler/lib/src/io/start_end_information.dart b/pkg/compiler/lib/src/io/start_end_information.dart
index f7d4dce1369fc7e34041cc999e43ae1d866742e3..71a3aec938bfb458bc3b69a14b6d9375f79f6cf2 100644
--- a/pkg/compiler/lib/src/io/start_end_information.dart
+++ b/pkg/compiler/lib/src/io/start_end_information.dart
@@ -129,8 +129,27 @@ class StartEndSourceInformationProcessor extends SourceInformationProcessor {
   /// registered for the top-most node with source information.
   bool hasRegisteredRoot = false;
 
+  /// The root of the tree. Used to add a [NoSourceLocationMarker] to the start
+  /// of the output.
+  js.Node root;
+
+  /// The root of the current subtree with source information. Used to add
+  /// [NoSourceLocationMarker] after areas with source information.
+  js.Node subRoot;
+
   StartEndSourceInformationProcessor(this.sourceMapper);
 
+  void onStartPosition(js.Node node, int startPosition) {
+    if (root == null) {
+      root = node;
+      sourceMapper.register(
+          node, startPosition, const NoSourceLocationMarker());
+    }
+    if (subRoot == null && node.sourceInformation != null) {
+      subRoot = node;
+    }
+  }
+
   @override
   void onPositions(
       js.Node node, int startPosition, int endPosition, int closingPosition) {
@@ -145,6 +164,11 @@ class StartEndSourceInformationProcessor extends SourceInformationProcessor {
         sourceMapper.register(node, endPosition, null);
         hasRegisteredRoot = true;
       }
+      if (node == subRoot) {
+        sourceMapper.register(
+            node, endPosition, const NoSourceLocationMarker());
+        subRoot = null;
+      }
     }
   }
 }