add fasta.scanner support for lazy assignment operators

pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart

Index: pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart b/pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart
index 0ab8ca2226dc925f8de2cdfa0a9835208ed72413..221fac2832b7a474b06f54b80aa4ac1b1c0d986d 100644
--- a/pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/utf8_bytes_scanner.dart
@@ -80,8 +80,11 @@ class Utf8BytesScanner extends ArrayBasedScanner {
    * is not the case, the entire array is copied before scanning.
    */
   Utf8BytesScanner(this.bytes,
-      {bool includeComments: false, bool scanGenericMethodComments: false})
+      {bool includeComments: false,
+      bool scanGenericMethodComments: false,
+      bool scanLazyAssignmentOperators: false})
       : super(includeComments, scanGenericMethodComments,
+            scanLazyAssignmentOperators,
             numberOfBytesHint: bytes.length) {
     assert(bytes.last == 0);
     // Skip a leading BOM.