Fix enabling of the new dart backend

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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 1363 matching lines @@
         // when these are handled as erroneous libraries/compilation units.
         compileLoadedLibraries();
       }
     });
   }
 
   bool irEnabled() {
     // TODO(sigurdm,kmillikin): Support checked-mode checks.
     return const bool.fromEnvironment('USE_NEW_BACKEND') &&
         backend is DartBackend &&
-        enableTypeAssertions &&
-        enableConcreteTypeInference;
+        !enableTypeAssertions &&
+        !enableConcreteTypeInference;
   }
 
   void computeMain() {
     if (mainApp == null) return;
 
     Element main = mainApp.findExported(MAIN);
     ErroneousElement errorElement = null;
     if (main == null) {
       if (analyzeOnly) {
         if (!analyzeAll) {
@@ skipping 799 matching lines @@
   int warnings = 0;
   int hints = 0;
 }
 
 class GenericTask extends CompilerTask {
   final String name;
 
   GenericTask(this.name, Compiler compiler)
       : super(compiler);
 }