move => bind this workaround to js_ast

lib/src/js/printer.dart

Index: lib/src/js/printer.dart
diff --git a/lib/src/js/printer.dart b/lib/src/js/printer.dart
index 0b76cc62052d9cc8c15e677c987e20238378236f..7491fae1485fb16abdc3d3bba1c7efb5e9dc9935 100644
--- a/lib/src/js/printer.dart
+++ b/lib/src/js/printer.dart
@@ -824,6 +824,9 @@ class Printer implements NodeVisitor {
   }
 
   visitArrowFun(ArrowFun fun) {
+    if (fun.bindThisWorkaround) {
+      out("(");
+    }
     localNamer.enterScope(fun);
     out("(");
     if (fun.params != null) {
@@ -840,6 +843,9 @@ class Printer implements NodeVisitor {
       blockBody(fun.body, needsSeparation: false, needsNewline: false);
     }
     localNamer.leaveScope();
+    if (fun.bindThisWorkaround) {
+      out(").bind(this)");
+    }
   }
 
   visitLiteralBool(LiteralBool node) {