Enable conditional directives by default.

pkg/compiler/lib/src/compiler.dart

Index: pkg/compiler/lib/src/compiler.dart
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index a05bcc787bf33a19116350b43ed642eae33ea25e..a175fe4433a0262eb28d5cbbdefeb657247ec557 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -399,8 +399,7 @@ abstract class Compiler implements LibraryLoaderListener {
     }
 
     tasks = [
-      dietParser = new DietParserTask(
-          this, enableConditionalDirectives: options.enableConditionalDirectives),
+      dietParser = new DietParserTask(this),
       scanner = createScannerTask(),
       serialization = new SerializationTask(this),
       libraryLoader = new LibraryLoaderTask(this,
@@ -410,10 +409,8 @@ abstract class Compiler implements LibraryLoaderListener {
           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),