chrome.bluetoothSocket: Fix regression in send()

In https://crrev.com/c/997098, params_ was changed to a local variable,
but it needs to last longer than that since net::WrappedIOBuffer may use
the data after the local variable goes out of scope.

This CL changed it back to be an instance variable.

Bug: 851799
Change-Id: I392f8acaef4c6473d6ea4fbee7209445aa09112e
Reviewed-on: https://chromium-review.googlesource.com/1103676
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Sonny Sasaka <sonnysasaka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568137}
void BluetoothSocketListenFunction::OnCreateServiceError(
    const std::string& message) {
  DCHECK_CURRENTLY_ON(work_thread_id());
  Respond(Error(message));
}

void BluetoothSocketListenFunction::OnCreateServiceError(
    const std::string& message) {
  DCHECK_CURRENTLY_ON(work_thread_id());
  Respond(Error(message));
}
