Add DCHECK to ensure IndexedDBDispatcher doesn't get re-created.

This could happen if there are IDB objects that survive the call to
didStopWorkerRunLoop.

BUG=121734
TEST=


Review URL: http://codereview.chromium.org/9999035

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@131679 0039d316-1c4b-4281-b951-d872f2087c98
void IndexedDBDispatcher::OnAbort(int32 thread_id, int32 transaction_id) {
  DCHECK_EQ(thread_id, CurrentWorkerId());
  WebIDBTransactionCallbacks* callbacks =
      pending_transaction_callbacks_.Lookup(transaction_id);
  if (!callbacks)
    return;
  callbacks->onAbort();
  pending_transaction_callbacks_.Remove(transaction_id);
}

void IndexedDBDispatcher::OnAbort(int32 thread_id, int32 transaction_id) {
  DCHECK_EQ(thread_id, CurrentWorkerId());
  WebIDBTransactionCallbacks* callbacks =
      pending_transaction_callbacks_.Lookup(transaction_id);
  if (!callbacks)
    return;
  callbacks->onAbort();
  pending_transaction_callbacks_.Remove(transaction_id);
}
