Enable conditional directives by default.

pkg/compiler/lib/src/parser/diet_parser_task.dart

Index: pkg/compiler/lib/src/parser/diet_parser_task.dart
diff --git a/pkg/compiler/lib/src/parser/diet_parser_task.dart b/pkg/compiler/lib/src/parser/diet_parser_task.dart
index 9afc8d4dcb90e6f532ce029a5d19aaad3aaa18f7..1df3a4c139bc6f6c7173d233dc15e25435441ec0 100644
--- a/pkg/compiler/lib/src/parser/diet_parser_task.dart
+++ b/pkg/compiler/lib/src/parser/diet_parser_task.dart
@@ -23,11 +23,8 @@ import 'partial_parser.dart' show
     PartialParser;
 
 class DietParserTask extends CompilerTask {
-  final bool _enableConditionalDirectives;
 
-  DietParserTask(Compiler compiler, {bool enableConditionalDirectives})
-      : this._enableConditionalDirectives = enableConditionalDirectives,
-        super(compiler);
+  DietParserTask(Compiler compiler) : super(compiler);
 
   final String name = 'Diet Parser';
 
@@ -39,8 +36,7 @@ class DietParserTask extends CompilerTask {
               compilationUnit.library));
       ElementListener listener = new ElementListener(
           scannerOptions, compiler.reporter, compilationUnit, idGenerator);
-      PartialParser parser = new PartialParser(
-          listener, enableConditionalDirectives: _enableConditionalDirectives);
+      PartialParser parser = new PartialParser(listener);
       try {
         parser.parseUnit(tokens);
       } on ParserError catch(_) {