[Fetch API] Fix redirect leak on "no-cors" requests

The spec issue is now fixed, and this CL follows the spec change[1].

1: https://github.com/whatwg/fetch/commit/14858d3e9402285a7ff3b5e47a22896ff3adc95d

Bug: 791324
Change-Id: Ic3e3955f43578b38fc44a5a6b2a1b43d56a2becb
Reviewed-on: https://chromium-review.googlesource.com/1023613
Reviewed-by: Tsuyoshi Horo <horo@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552964}
void FetchManager::Loader::Dispose() {
  probe::detachClientRequest(execution_context_, this);
  fetch_manager_ = nullptr;
  if (threadable_loader_) {
    if (fetch_request_data_->Keepalive())
      threadable_loader_->Detach();
    else
      threadable_loader_->Cancel();
    threadable_loader_ = nullptr;
  }
  if (integrity_verifier_)
    integrity_verifier_->Cancel();
  execution_context_ = nullptr;
}

void FetchManager::Loader::Dispose() {
  probe::detachClientRequest(execution_context_, this);
  fetch_manager_ = nullptr;
  if (threadable_loader_) {
    if (fetch_request_data_->Keepalive())
      threadable_loader_->Detach();
    else
      threadable_loader_->Cancel();
    threadable_loader_ = nullptr;
  }
  if (integrity_verifier_)
    integrity_verifier_->Cancel();
  execution_context_ = nullptr;
}
