add fasta.scanner support for lazy assignment operators

pkg/front_end/test/scanner_fasta_test.dart

Index: pkg/front_end/test/scanner_fasta_test.dart
diff --git a/pkg/front_end/test/scanner_fasta_test.dart b/pkg/front_end/test/scanner_fasta_test.dart
index a588b63b78d80409a0be8efba4c9b642f35ba35e..9404a293ef8fdd24a9dbc46fc056dfc4a7871469 100644
--- a/pkg/front_end/test/scanner_fasta_test.dart
+++ b/pkg/front_end/test/scanner_fasta_test.dart
@@ -28,31 +28,15 @@ class ScannerTest_Fasta extends ScannerTestBase {
   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(paulberry): once lazyAssignmentOperators are fully supported by
-    // Dart, remove this flag.
-    var scanner = new fasta.StringScanner(source, includeComments: true);
-    scanner.scanGenericMethodComments = genericMethodComments;
+    var scanner = new fasta.StringScanner(source,
+        includeComments: true,
+        scanGenericMethodComments: genericMethodComments,
+        scanLazyAssignmentOperators: lazyAssignmentOperators);
     var token = scanner.tokenize();
     return new ToAnalyzerTokenStreamConverter_WithListener(listener)
         .convertTokens(token);
   }
 
-  @override
-  @failingTest
-  void test_ampersand_ampersand_eq() {
-    // TODO(paulberry,ahe): Fasta doesn't support `&&=` yet
-    super.test_ampersand_ampersand_eq();
-  }
-
-  @override
-  @failingTest
-  void test_bar_bar_eq() {
-    // TODO(paulberry,ahe): Fasta doesn't support `||=` yet
-    super.test_bar_bar_eq();
-  }
-
   void test_comments() {
     const source = '''
        /// Doc comment before class