Ensure that collectedClasses always contains a [globalObject, descriptor] pair.

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart

Index: pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index ffc7b01cae5efa5e4e54fc0973945b387fadb50c..bd3f27158bb25790a4857e3c8f7f1af8f4c169b2 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -1194,8 +1194,7 @@ class OldEmitter implements Emitter {
           #constructorName.builtin$cls = #constructorNameString;
           if (!"name" in #constructorName)
               #constructorName.name = #constructorNameString;
-          $desc = $collectedClasses.#constructorName;
-          if ($desc instanceof Array) $desc = $desc[1];
+          $desc = $collectedClasses.#constructorName[1];
           #constructorName.prototype = $desc;
           ''' /* next string is not a raw string */ '''
           if (#hasIsolateSupport) {