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

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 fad4298d35af97a8d80cc6d5b4c10ba27292c562..f792bfa48bc3ffb7552eb3d051e83af55a55325d 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -716,6 +716,8 @@ abstract class Compiler implements DiagnosticListener {
   /// suppressed for each library.
   Map<Uri, SuppressionInfo> suppressedWarnings = <Uri, SuppressionInfo>{};
 
+  static const bool USE_CPS_IR = const bool.fromEnvironment("USE_CPS_IR");

[floitsch, 2014/11/12 11:03:19]

Just move it to js_backend/backend.dart unless you think other parts of dart2js
need to have access to it. (But they shouldn't).

[sigurdm, 2014/11/13 08:29:41]

Done.

+
   final bool suppressWarnings;
 
   /// `true` if async/await features are supported.