Fire window.onerror for uncaught IndexedDB errors

LayoutTests/storage/indexeddb/resources/request-continue-abort.js

 if (this.importScripts) {
     importScripts('../../../resources/js-test.js');
     importScripts('shared.js');
 }
 
 description("Regression test for IDBRequest issue calling continue on a cursor then aborting.");
 
 indexedDBTest(prepareDatabase, testCursor);
 function prepareDatabase()
 {
@@ skipping 18 matching lines @@
     debug("");
     evalAndLog("state = 0");
     evalAndLog("request = store.openCursor()");
     request.onsuccess = function() {
         debug("");
         debug("'success' event fired at request.");
         shouldBe("++state", "1");
         evalAndLog("request.result.continue()");
         transaction.abort();
     };
-    request.onerror = function() {
+    request.onerror = function(evt) {
+        evt.preventDefault();
         debug("");
         debug("'error' event fired at request.");
         shouldBe("++state", "2");
     };
     transaction.oncomplete = unexpectedCompleteCallback;
     transaction.onabort = function() {
         debug("");
         debug("'abort' event fired at transaction.");
         shouldBe("++state", "3");
         finishJSTest();
     };
 }