Add missing USED_FROM_MULTIPLE_THREADS(IDBVersionChangeEvent) decl.

indexeddb is available in Worker contexts, including this event.

R=
BUG=340522

Review URL: https://codereview.chromium.org/185323003

git-svn-id: svn://svn.chromium.org/blink/trunk@168246 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/heap/ThreadState.h

@@ -556,6 +556,7 @@ USED_FROM_MULTIPLE_THREADS(ErrorEvent);
 USED_FROM_MULTIPLE_THREADS(Event);
 USED_FROM_MULTIPLE_THREADS(EventSource);
 USED_FROM_MULTIPLE_THREADS(EventTarget);
+USED_FROM_MULTIPLE_THREADS(IDBVersionChangeEvent);
 USED_FROM_MULTIPLE_THREADS(Key);
 USED_FROM_MULTIPLE_THREADS(KeyAlgorithm);
 USED_FROM_MULTIPLE_THREADS(KeyPair);