Enable conditional directives by default.

pkg/compiler/lib/src/compiler.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.compiler_base;
 
 import 'dart:async' show
     EventSink,
     Future;
 
@@ skipping 381 matching lines @@
       backend = jsBackend;
     } else {
       backend = new dart_backend.DartBackend(this, options.strips,
           multiFile: options.dart2dartMultiFile);
       if (options.dumpInfo) {
         throw new ArgumentError('--dump-info is not supported for dart2dart.');
       }
     }
 
     tasks = [
-      dietParser = new DietParserTask(
-          this, enableConditionalDirectives: options.enableConditionalDirectives),
+      dietParser = new DietParserTask(this),
       scanner = createScannerTask(),
       serialization = new SerializationTask(this),
       libraryLoader = new LibraryLoaderTask(this,
           new _ResolvedUriTranslator(this),
           new _ScriptLoader(this),
           new _ElementScanner(scanner),
           this.serialization,
           this,
           environment),
-      parser = new ParserTask(this,
-          enableConditionalDirectives: options.enableConditionalDirectives),
-      patchParser = new PatchParserTask(
-          this, enableConditionalDirectives: options.enableConditionalDirectives),
+      parser = new ParserTask(this),
+      patchParser = new PatchParserTask(this),
       resolver = createResolverTask(),
       closureToClassMapper = new closureMapping.ClosureTask(this),
       checker = new TypeCheckerTask(this),
       typesTask = new ti.TypesTask(this),
       constants = backend.constantCompilerTask,
       deferredLoadTask = new DeferredLoadTask(this),
       mirrorUsageAnalyzerTask = new MirrorUsageAnalyzerTask(this),
       enqueuer = new EnqueueTask(this),
       dumpInfoTask = new DumpInfoTask(this),
       reuseLibraryTask = new GenericTask('Reuse library', this),
@@ skipping 1730 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }