Enable conditional directives by default.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.parser;
 
 import '../options.dart' show ParserOptions;
 import '../common.dart';
 import '../tokens/keyword.dart' show Keyword;
 import '../tokens/precedence.dart' show PrecedenceInfo;
@@ skipping 165 matching lines @@
     Token semicolon = token;
     token = expect(';', token);
     listener.endImport(importKeyword, deferredKeyword, asKeyword, semicolon);
     return token;
   }
 
   /// if (test) uri
   Token parseConditionalUris(Token token) {
     listener.beginConditionalUris(token);
     int count = 0;
-    if (parserOptions.enableConditionalDirectives) {
-      while (optional('if', token)) {
-        count++;
-        token = parseConditionalUri(token);
-      }
+    while (optional('if', token)) {
+      count++;
+      token = parseConditionalUri(token);
     }
     listener.endConditionalUris(count);
     return token;
   }
 
   Token parseConditionalUri(Token token) {
     listener.beginConditionalUri(token);
     Token ifKeyword = token;
     token = expect('if', token);
     token = expect('(', token);
@@ skipping 2783 matching lines @@
     }
     listener.handleContinueStatement(hasTarget, continueKeyword, token);
     return expectSemicolon(token);
   }
 
   Token parseEmptyStatement(Token token) {
     listener.handleEmptyStatement(token);
     return expectSemicolon(token);
   }
 }