Add a command line option to use the new CPS based 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 700 matching lines @@
    * If true, stop compilation after type inference is complete. Used for
    * debugging and testing purposes only.
    */
   bool stopAfterTypeInference = false;
 
   /**
    * If [:true:], comment tokens are collected in [commentMap] during scanning.
    */
   final bool preserveComments;
 
+  /// Use the new CPS based backend end.  This flag works for both the Dart and
+  /// JavaScript backend.
+  final bool useCpsIr;
+
   /**
    * Is the compiler in verbose mode.
    */
   final bool verbose;
 
   /**
    * URI of the main source map if the compiler is generating source
    * maps.
    */
   final Uri sourceMapUri;
@@ skipping 262 matching lines @@
             this.preserveUris: false,
             this.enableNativeLiveTypeAnalysis: false,
             bool emitJavaScript: true,
             bool dart2dartMultiFile: false,
             bool generateSourceMap: true,
             bool analyzeAllFlag: false,
             bool analyzeOnly: false,
             this.analyzeMain: false,
             bool analyzeSignaturesOnly: false,
             this.preserveComments: false,
+            this.useCpsIr: false,
             this.verbose: false,
             this.sourceMapUri: null,
             this.outputUri: null,
             this.buildId: UNDETERMINED_BUILD_ID,
             this.terseDiagnostics: false,
             this.deferredMapUri: null,
             this.dumpInfo: false,
             this.showPackageWarnings: false,
             this.useContentSecurityPolicy: false,
             this.suppressWarnings: false,
@@ skipping 450 matching lines @@
           mainApp = library;
         });
       }
     }).then((_) {
       compileLoadedLibraries();
     });
   }
 
   bool irEnabled() {
     // TODO(sigurdm,kmillikin): Support checked-mode checks.
-    return const bool.fromEnvironment('USE_NEW_BACKEND') &&
+    return useCpsIr &&
         backend is DartBackend &&
         !enableTypeAssertions &&
         !enableConcreteTypeInference;
   }
 
   void computeMain() {
     if (mainApp == null) return;
 
     Element main = mainApp.findExported(MAIN);
     ErroneousElement errorElement = null;
@@ skipping 932 matching lines @@
     return futureClass.computeType(compiler).createInstantiation([elementType]);
   }
 
   @override
   InterfaceType streamType([DartType elementType = const DynamicType()]) {
     return streamClass.computeType(compiler).createInstantiation([elementType]);
   }
 }
 
 typedef void InternalErrorFunction(Spannable location, String message);