Add a command line option to use the new CPS based backend.

pkg/compiler/lib/src/dart2js.dart

Index: pkg/compiler/lib/src/dart2js.dart
diff --git a/pkg/compiler/lib/src/dart2js.dart b/pkg/compiler/lib/src/dart2js.dart
index 2c46faab1e1d297184ea9e57e04c028229f0b191..5469e39dc07d37632abcb02073fed8a9ac40c342 100644
--- a/pkg/compiler/lib/src/dart2js.dart
+++ b/pkg/compiler/lib/src/dart2js.dart
@@ -302,6 +302,7 @@ Future<api.CompilationResult> compile(List<String> argv) {
     new OptionHandler(
         '--output-type=dart|--output-type=dart-multi|--output-type=js',
         setOutputType),
+    new OptionHandler('--use-cps-ir', passThrough),
     new OptionHandler('--verbose', setVerbose),
     new OptionHandler('--version', (_) => wantVersion = true),
     new OptionHandler('--library-root=.+', setLibraryRoot),
@@ -630,6 +631,9 @@ be removed in a future version:
   --generate-code-with-compile-time-errors
     Generates output even if the program contains compile-time errors. Use the
     exit code to determine if compilation failed.
+
+  --use-cps-ir
+    Experimental.  Use the new CPS based backend for code generation.
 '''.trim());
 }