Enable conditional directives by default.

pkg/analyzer_cli/lib/src/driver.dart

Index: pkg/analyzer_cli/lib/src/driver.dart
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index f3016d56ba06af436d9433795b820e32d98233c1..68b62c24c353a91f2901143cf6ab6c42cc0e72a5 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -298,10 +298,6 @@ class Driver implements CommandLineStarter {
     if (options.enableSuperMixins != _previousOptions.enableSuperMixins) {
       return false;
     }
-    if (options.enableConditionalDirectives !=
-        _previousOptions.enableConditionalDirectives) {
-      return false;
-    }
     return true;
   }
 
@@ -603,8 +599,6 @@ class Driver implements CommandLineStarter {
     contextOptions.hint = !options.disableHints;
     contextOptions.enableStrictCallChecks = options.enableStrictCallChecks;
     contextOptions.enableSuperMixins = options.enableSuperMixins;
-    contextOptions.enableConditionalDirectives =
-        options.enableConditionalDirectives;
     contextOptions.generateImplicitErrors = options.showPackageWarnings;
     contextOptions.generateSdkErrors = options.showSdkWarnings;
     contextOptions.lint = options.lints;