Enable conditional directives by default.

pkg/analyzer/lib/src/task/options.dart

Index: pkg/analyzer/lib/src/task/options.dart
diff --git a/pkg/analyzer/lib/src/task/options.dart b/pkg/analyzer/lib/src/task/options.dart
index 8c6980b7fac9be931488ca0b6e489b1efac1a540..9539abea533fcf611ec6d5adb555577151a4ec8f 100644
--- a/pkg/analyzer/lib/src/task/options.dart
+++ b/pkg/analyzer/lib/src/task/options.dart
@@ -48,8 +48,6 @@ class AnalyzerOptions {
   static const String enableGenericMethods = 'enableGenericMethods';
   static const String enableStrictCallChecks = 'enableStrictCallChecks';
   static const String enableSuperMixins = 'enableSuperMixins';
-  static const String enableConditionalDirectives =
-      "enableConditionalDirectives";
   static const String errors = 'errors';
   static const String exclude = 'exclude';
   static const String language = 'language';
@@ -81,7 +79,6 @@ class AnalyzerOptions {
   /// Supported `analyzer` language configuration options.
   static const List<String> languageOptions = const [
     enableAsync,
-    enableConditionalDirectives,
     enableGenericMethods,
     enableStrictCallChecks,
     enableSuperMixins
@@ -503,14 +500,6 @@ class _OptionsProcessor {
         context.analysisOptions = options;
       }
     }
-    if (feature == AnalyzerOptions.enableConditionalDirectives) {
-      if (isTrue(value)) {
-        AnalysisOptionsImpl options =
-            new AnalysisOptionsImpl.from(context.analysisOptions);
-        options.enableConditionalDirectives = true;
-        context.analysisOptions = options;
-      }
-    }
   }
 
   void setLanguageOptions(AnalysisContext context, Object configs) {