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..0d924678759e808f1820d61abf1fc6fb33740474 100644
--- a/pkg/front_end/test/scanner_fasta_test.dart
+++ b/pkg/front_end/test/scanner_fasta_test.dart
@@ -28,31 +28,14 @@ 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

[Paul Berry, 2017/05/20 13:57:10]

Don't remove this TODO--it still applies (we should still remove the
`lazyAssignmentOperators` flag once they are fully supported by Dart)

[danrubel, 2017/05/20 21:17:04]

Good point. I moved the comment from here to the
fasta.scanner.scanLazyAssignmentOperators field because we probably want to
remove that field and all direct and indirect references once the language has
been updated.

-    // Dart, remove this flag.
     var scanner = new fasta.StringScanner(source, includeComments: true);
     scanner.scanGenericMethodComments = genericMethodComments;
+    scanner.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