Block a compromised renderer from reusing request ids.

BUG=578882

Review URL: https://codereview.chromium.org/1608573002

Cr-Commit-Position: refs/heads/master@{#372547}
void ResourceDispatcherHostImpl::RemovePendingLoader(
    const LoaderMap::iterator& iter) {
  ResourceRequestInfoImpl* info = iter->second->GetRequestInfo();

  IncrementOutstandingRequestsMemory(-1, *info);

  pending_loaders_.erase(iter);
}

void ResourceDispatcherHostImpl::RemovePendingLoader(
    const LoaderMap::iterator& iter) {
  ResourceRequestInfoImpl* info = iter->second->GetRequestInfo();

  IncrementOutstandingRequestsMemory(-1, *info);

  pending_loaders_.erase(iter);
}
