dart2js: Fix checked mode error in nameForGetOneShotInterceptor.

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

Index: pkg/compiler/lib/src/js_backend/minify_namer.dart
diff --git a/pkg/compiler/lib/src/js_backend/minify_namer.dart b/pkg/compiler/lib/src/js_backend/minify_namer.dart
index 3e9ae73ba3252a544b17c774eeb92f4afd170eb5..b781bc0ad0eb9a8155c638cb272e0a126a786f64 100644
--- a/pkg/compiler/lib/src/js_backend/minify_namer.dart
+++ b/pkg/compiler/lib/src/js_backend/minify_namer.dart
@@ -343,7 +343,8 @@ abstract class _MinifiedOneShotInterceptorNamer implements Namer {
         ? r"$get"
         : selector.isSetter ? r"$set" : "";
     String callSuffix =
-        selector.isCall ? callSuffixForStructure(selector.callStructure) : "";
+        selector.isCall ? callSuffixForStructure(selector.callStructure).join()
+                        : "";
     String suffix = suffixForGetInterceptor(classes);
     String fullName = "\$intercepted$prefix\$$root$callSuffix\$$suffix";
     return _disambiguateInternalGlobal(fullName);