Support conditional directives in the options file.

pkg/analyzer/test/src/task/options_test.dart

Index: pkg/analyzer/test/src/task/options_test.dart
diff --git a/pkg/analyzer/test/src/task/options_test.dart b/pkg/analyzer/test/src/task/options_test.dart
index ebdca704569074a62dbe46923a3cc7f3e78bb321..105ed8b46f977f0418004fbb4695bf15bf09c497 100644
--- a/pkg/analyzer/test/src/task/options_test.dart
+++ b/pkg/analyzer/test/src/task/options_test.dart
@@ -77,6 +77,16 @@ analyzer:
     expect(analysisOptions.enableGenericMethods, true);
   }
 
+  test_configure_enableConditionalDirectives() {
+    expect(analysisOptions.enableConditionalDirectives, false);
+    configureContext('''
+analyzer:
+  language:
+    enableConditionalDirectives: true
+''');
+    expect(analysisOptions.enableConditionalDirectives, true);
+  }
+
   test_configure_enableSuperMixins() {
     configureContext('''
 analyzer: