Remove FrameDeleted(nullptr) from AudioLoopbackStreamCreator

Reasonably, nullptr isn't a frame, so it cannot be deleted.
This call also isn't necessary, since the destructor of |factory_|
is going to clean everything up soon anyways.

Adds a DCHECK to ForwardingAudioStreamFactory::FrameDeleted to assert
that |render_frame_host| is non-null.

Bug: 734672
Change-Id: Ide1679e93923b70182498f57b92eb21f08f8e5f6
Reviewed-on: https://chromium-review.googlesource.com/1256962Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595854}

content/browser/media/forwarding_audio_stream_factory.cc

@@ -179,17 +179,17 @@ const base::UnguessableToken& ForwardingAudioStreamFactory::GetGroupID() {
 void ForwardingAudioStreamFactory::FrameDeleted(
     RenderFrameHost* render_frame_host) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK(render_frame_host);
   CleanupStreamsBelongingTo(render_frame_host);
 }
 
 void ForwardingAudioStreamFactory::CleanupStreamsBelongingTo(
     RenderFrameHost* render_frame_host) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  DCHECK(render_frame_host);
 
-  const int process_id =
-      render_frame_host ? render_frame_host->GetProcess()->GetID() : -1;
-  const int frame_id =
-      render_frame_host ? render_frame_host->GetRoutingID() : -1;
+  const int process_id = render_frame_host->GetProcess()->GetID();
+  const int frame_id = render_frame_host->GetRoutingID();
 
   TRACE_EVENT_BEGIN2("audio", "CleanupStreamsBelongingTo", "group",
                      group_id_.GetLowForSerialization(), "process id",

content/browser/media/in_process_audio_loopback_stream_creator.cc

@@ -70,7 +70,6 @@ InProcessAudioLoopbackStreamCreator::InProcessAudioLoopbackStreamCreator()
 
 InProcessAudioLoopbackStreamCreator::~InProcessAudioLoopbackStreamCreator() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
-  factory_.FrameDeleted(nullptr);
 }
 
 void InProcessAudioLoopbackStreamCreator::CreateLoopbackStream(