Set up a stub pipline for using the new cps-based ir to generate js.

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 1349 matching lines @@
       }
     }).then((_) {
       if (!compilationFailed) {
         // TODO(johnniwinther): Reenable analysis of programs with load failures
         // 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;
+  }
+
   void computeMain() {
     if (mainApp == null) return;
 
     Element main = mainApp.findExported(MAIN);
     ErroneousElement errorElement = null;
     if (main == null) {
       if (analyzeOnly) {
         if (!analyzeAll) {
           errorElement = new ErroneousElementX(
               MessageKind.CONSIDER_ANALYZE_ALL, {'main': MAIN}, MAIN, mainApp);
@@ skipping 102 matching lines @@
     assert(mainFunction != null);
     phase = PHASE_DONE_RESOLVING;
 
     world.populate();
     // Compute whole-program-knowledge that the backend needs. (This might
     // require the information computed in [world.populate].)
     backend.onResolutionComplete();
 
     deferredLoadTask.onResolutionComplete(mainFunction);
 
-    log('Building IR...');
-    irBuilder.buildNodes();
+    if (irEnabled()) {
+      log('Building IR...');
+      irBuilder.buildNodes();
+    }
 
     log('Inferring types...');
     typesTask.onResolutionComplete(mainFunction);
 
     if (stopAfterTypeInference) return;
 
     log('Compiling...');
     phase = PHASE_COMPILING;
     // TODO(johnniwinther): Move these to [CodegenEnqueuer].
     if (hasIsolateSupport) {
@@ skipping 671 matching lines @@
   int warnings = 0;
   int hints = 0;
 }
 
 class GenericTask extends CompilerTask {
   final String name;
 
   GenericTask(this.name, Compiler compiler)
       : super(compiler);
 }