Fixing double-completing indexed DB transactions

sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart

Index: sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
diff --git a/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart b/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
index 5b2948dfec31367eac7ea807fb43b75fa684ea90..d0b2919771fa1d7af3324d4cd5366f0d961480af 100644
--- a/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
+++ b/sdk/lib/indexed_db/dart2js/indexed_db_dart2js.dart
@@ -1252,16 +1252,22 @@ class Transaction extends EventTarget native "IDBTransaction" {
   Future<Database> get completed {
     var completer = new Completer<Database>();
 
+    var errored = false;
+
     this.onComplete.first.then((_) {
       completer.complete(db);
     });
 
     this.onError.first.then((e) {
+      errored = true;
       completer.completeError(e);
     });
 
     this.onAbort.first.then((e) {
-      completer.completeError(e);
+      // Avoid completing twice if an error occurs.
+      if (!errored) {

[Emily Fortuna, 2013/10/16 00:20:59]

would completer.isCompleted work instead?

[blois, 2013/10/17 01:05:07]

Ah, much nicer!

+        completer.completeError(e);
+      }
     });
 
     return completer.future;