Always parse 'x.y' as a prefixed identifier.

pkg/analyzer/test/generated/parser_test.dart

Index: pkg/analyzer/test/generated/parser_test.dart
diff --git a/pkg/analyzer/test/generated/parser_test.dart b/pkg/analyzer/test/generated/parser_test.dart
index ae8b9c2dcea64032ae3917dd8aa1a64c29c59f7b..4a26ac12896ba3b8b7fbdef790f34e994d60b40f 100644
--- a/pkg/analyzer/test/generated/parser_test.dart
+++ b/pkg/analyzer/test/generated/parser_test.dart
@@ -4180,11 +4180,11 @@ abstract class ExpressionParserTestMixin implements AbstractParserTestCase {
     Expression expression = parseAssignableExpression('x.y', false);
     expect(expression, isNotNull);
     assertNoErrors();
-    var propertyAccess = expression as PropertyAccess;
-    expect(propertyAccess.target, isNotNull);
-    expect(propertyAccess.operator, isNotNull);
-    expect(propertyAccess.operator.type, TokenType.PERIOD);
-    expect(propertyAccess.propertyName, isNotNull);
+    var identifier = expression as PrefixedIdentifier;
+    expect(identifier.prefix.name, 'x');
+    expect(identifier.period, isNotNull);
+    expect(identifier.period.type, TokenType.PERIOD);
+    expect(identifier.identifier.name, 'y');
   }
 
   void test_parseAssignableExpression_identifier_index() {