Handle the case of detached iframe in RendererWebAudioDeviceImpl

DCHECK in RendererWebAudioDeviceImpl assumes an AudioContext to have
a valid frame ID, and it makes DCHECK-enabled build crash when an
AudioContext is originated from a detached iframe.

This CL loosens the condition of DCHECK to allow such case.

Bug: 954995
Change-Id: I50b577f0e0b466ed76c0d9bbb807cd10adb30acd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1577841Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Hongchan Choi <hongchan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653326}

content/renderer/media/renderer_webaudiodevice_impl.cc

@@ -133,7 +133,7 @@ RendererWebAudioDeviceImpl::RendererWebAudioDeviceImpl(
       session_id_(session_id),
       frame_id_(render_frame_id_cb.Run()) {
   DCHECK(client_callback_);
-  DCHECK_NE(frame_id_, MSG_ROUTING_NONE);
+  DCHECK(session_id_ == 0 || frame_id_ != MSG_ROUTING_NONE);
 
   media::AudioParameters hardware_params(
       device_params_cb.Run(frame_id_, session_id_, std::string()));