cps-ir: Support foreign code.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
index 4b3ea71e949e4270440e9e250e38eca38e082630..f287c4d7ef07dc5408d779d53cc9f924fb6b50fe 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
@@ -344,6 +344,14 @@ class SExpressionStringifier extends Indentation implements Visitor<String> {
     String args = node.arguments.map(access).join(' ');
     return '(ApplyBuiltinOperator $operator ($args))';
   }
+
+  @override
+  String visitForeignCode(ForeignCode node) {
+    String arguments = node.arguments.map(access).join(' ');
+    String continuation = node.continuation == null ? ''
+        : ' ${access(node.continuation)}';
+    return '(JS ${node.type} ${node.codeTemplate} ($arguments)$continuation)';
+  }
 }
 
 class ConstantStringifier extends ConstantValueVisitor<String, Null> {