add fasta.scanner support for lazy assignment operators

pkg/front_end/lib/src/fasta/scanner/string_scanner.dart

Index: pkg/front_end/lib/src/fasta/scanner/string_scanner.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/string_scanner.dart b/pkg/front_end/lib/src/fasta/scanner/string_scanner.dart
index 5ead4a5a438afcd696d44d9e53041f0b22d9ad8d..7f9c53ed9a1f301c0e48b0f4480333271fbd02ef 100644
--- a/pkg/front_end/lib/src/fasta/scanner/string_scanner.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/string_scanner.dart
@@ -22,9 +22,12 @@ class StringScanner extends ArrayBasedScanner {
   int scanOffset = -1;
 
   StringScanner(String string,
-      {bool includeComments: false, bool scanGenericMethodComments: false})
+      {bool includeComments: false,
+      bool scanGenericMethodComments: false,
+      bool scanLazyAssignmentOperators: false})
       : string = ensureZeroTermination(string),
-        super(includeComments, scanGenericMethodComments);
+        super(includeComments, scanGenericMethodComments,
+            scanLazyAssignmentOperators);
 
   static String ensureZeroTermination(String string) {
     return (string.isEmpty || string.codeUnitAt(string.length - 1) != 0)