add fasta.scanner support for lazy assignment operators

pkg/front_end/test/scanner_replacement_test.dart

Index: pkg/front_end/test/scanner_replacement_test.dart
diff --git a/pkg/front_end/test/scanner_replacement_test.dart b/pkg/front_end/test/scanner_replacement_test.dart
index e1d5908706d108fdb225550bc576bb0f97d035c1..772ad34247b4c6f1ee38c58d5aa0fc1cca03bbfa 100644
--- a/pkg/front_end/test/scanner_replacement_test.dart
+++ b/pkg/front_end/test/scanner_replacement_test.dart
@@ -35,12 +35,10 @@ class ScannerTest_Replacement extends ScannerTest {
   analyzer.Token scanWithListener(String source, ErrorListener listener,
       {bool genericMethodComments: false,
       bool lazyAssignmentOperators: false}) {
-    // Note: Fasta always supports lazy assignment operators (`&&=` and `||=`),
-    // so we can ignore the `lazyAssignmentOperators` flag.
-    // TODO(danrubel): once lazyAssignmentOperators are fully supported by
-    // Dart, remove this flag.
     fasta.ScannerResult result = fasta.scanString(source,
-        includeComments: true, scanGenericMethodComments: genericMethodComments,
+        includeComments: true,
+        scanGenericMethodComments: genericMethodComments,
+        scanLazyAssignmentOperators: lazyAssignmentOperators,
         recover: ((List<int> bytes, fasta.Token tokens, List<int> lineStarts) {
       // perform recovery as a separate step
       // so that the token stream can be validated before and after recovery
@@ -57,22 +55,6 @@ class ScannerTest_Replacement extends ScannerTest {
     return extractErrors(tokens, listener);
   }
 
-  @override
-  @failingTest
-  void test_ampersand_ampersand_eq() {
-    // TODO(paulberry,ahe): Fasta scanner doesn't support lazy assignment
-    // operators.
-    super.test_ampersand_ampersand_eq();
-  }
-
-  @override
-  @failingTest
-  void test_bar_bar_eq() {
-    // TODO(paulberry,ahe): Fasta scanner doesn't support lazy assignment
-    // operators.
-    super.test_bar_bar_eq();
-  }
-
   void _assertOpenClosePair(String source) {
     fasta.BeginGroupToken open = _scan(source);
     fasta.Token close = open.next;