js_runtime: help type inference of string replace

sdk/lib/_internal/js_runtime/lib/string_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/string_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/string_helper.dart b/sdk/lib/_internal/js_runtime/lib/string_helper.dart
index 8ec6c479974d43341439103b8a7cc1f21e16484c..78a0980cff9d66b8d7542f577746a3a89a4bcb45 100644
--- a/sdk/lib/_internal/js_runtime/lib/string_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/string_helper.dart
@@ -142,7 +142,7 @@ stringReplaceAllUnchecked(receiver, pattern, replacement) {
   if (pattern is String) {
     if (pattern == "") {
       if (receiver == "") {
-        return replacement;
+        return JS('String', '#', replacement); // help type inference.

[Siggi Cherem (dart-lang), 2017/01/23 17:45:04]

would it also work if we change the check in line 141 to be:

replacement = checkString(replacement); ?

       } else {
         StringBuffer result = new StringBuffer('');
         int length = receiver.length;