dart2js cps: Introduce '<<' operator in type propagation.

pkg/compiler/lib/src/js_backend/codegen/codegen.dart

Index: pkg/compiler/lib/src/js_backend/codegen/codegen.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
index 22a0707b418381284c886d1caf05c0ae7cdd6b18..2cd21cc5d1433a86a21b5039e23955134a35ef0d 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
@@ -800,6 +800,8 @@ class CodeGenerator extends tree_ir.StatementVisitor
         return new js.Binary('>', args[0], args[1]);
       case BuiltinOperator.NumGe:
         return new js.Binary('>=', args[0], args[1]);
+      case BuiltinOperator.NumShl:
+        return js.js('(# << #) >>> 0', args);
       case BuiltinOperator.StringConcatenate:
         if (args.isEmpty) return js.string('');
         return args.reduce((e1,e2) => new js.Binary('+', e1, e2));