Add AudioStreamRegistry. Move stream counting logic

content/browser/renderer_host/media/audio_stream_registry_impl.cc

Index: content/browser/renderer_host/media/audio_stream_registry_impl.cc
diff --git a/content/browser/renderer_host/media/audio_stream_registry_impl.cc b/content/browser/renderer_host/media/audio_stream_registry_impl.cc
new file mode 100644
index 0000000000000000000000000000000000000000..89ac580a85e99c822b617c37ea6047a0a0ecee4b
--- /dev/null
+++ b/content/browser/renderer_host/media/audio_stream_registry_impl.cc
@@ -0,0 +1,104 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.

[DaleCurtis, 2017/01/12 19:22:12]

I think instead all of this can be deleted. AudioStreamMonitor contains
everything needed to handle these cases now I think. It's notified when new
streams are added and fans out notifications when audio starts/stops. 

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/renderer_host/media/audio_stream_registry_impl.h"
+
+#include <algorithm>
+
+#include "base/lazy_instance.h"
+#include "base/metrics/histogram_macros.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/render_process_host.h"
+#include "media/audio/audio_streams_tracker.h"
+
+namespace content {
+
+namespace {
+
+base::LazyInstance<media::AudioStreamsTracker> g_audio_output_streams_tracker =
+    LAZY_INSTANCE_INITIALIZER;
+
+void NotifyRenderProcessHostThatAudioStateChanged(int render_process_id) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  RenderProcessHost* render_process_host =
+      RenderProcessHost::FromID(render_process_id);
+
+  if (render_process_host)
+    render_process_host->AudioStateChanged();
+}
+
+}  // namespace
+
+AudioStreamRegistryImpl::AudioStreamRegistryImpl(int render_process_id)
+    : render_process_id_(render_process_id) {}
+
+AudioStreamRegistryImpl::~AudioStreamRegistryImpl() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_EQ(num_output_streams_, 0);
+  DCHECK_EQ(num_playing_output_streams_, 0);
+
+  if (max_simultaneous_output_streams_ > 0) {
+    UMA_HISTOGRAM_CUSTOM_COUNTS("Media.AudioRendererIpcStreams",
+                                max_simultaneous_output_streams_, 1, 50, 51);
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "Media.AudioRendererIpcStreamsTotal",
+        g_audio_output_streams_tracker.Get().max_stream_count(), 1, 100, 101);
+    g_audio_output_streams_tracker.Get().ResetMaxStreamCount();
+  }
+}
+
+// static
+AudioStreamRegistryImpl::UniquePtr AudioStreamRegistryImpl::Create(
+    int render_process_id) {
+  return {new AudioStreamRegistryImpl(render_process_id), {}};
+}
+
+bool AudioStreamRegistryImpl::HasActiveAudio() {
+  return !base::AtomicRefCountIsZero(&num_playing_output_streams_);
+}
+
+void AudioStreamRegistryImpl::RegisterStream() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  ++num_output_streams_;
+  max_simultaneous_output_streams_ =
+      std::max(max_simultaneous_output_streams_, num_output_streams_);
+  g_audio_output_streams_tracker.Get().IncreaseStreamCount();
+}
+
+void AudioStreamRegistryImpl::DeregisterStream() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  DCHECK_GT(num_output_streams_, 0);
+  --num_output_streams_;
+  g_audio_output_streams_tracker.Get().DecreaseStreamCount();
+}
+
+void AudioStreamRegistryImpl::StreamStateChanged(bool playing) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  if (playing) {
+    base::AtomicRefCountInc(&num_playing_output_streams_);
+
+    // Inform the RenderProcessHost when audio starts playing for the first
+    // time. The nonatomic increment-and-read is ok since this is the only
+    // thread that |num_playing_output_streams_| may be updated on.
+    if (base::AtomicRefCountIsOne(&num_playing_output_streams_)) {
+      BrowserThread::PostTask(
+          BrowserThread::UI, FROM_HERE,
+          base::Bind(&NotifyRenderProcessHostThatAudioStateChanged,
+                     render_process_id_));
+    }
+  } else {
+    // Inform the RenderProcessHost when there is no more audio playing.
+    DCHECK(!base::AtomicRefCountIsZero(&num_playing_output_streams_));
+    if (!base::AtomicRefCountDec(&num_playing_output_streams_)) {
+      BrowserThread::PostTask(
+          BrowserThread::UI, FROM_HERE,
+          base::Bind(&NotifyRenderProcessHostThatAudioStateChanged,
+                     render_process_id_));
+    }
+  }
+  DCHECK_LE(num_playing_output_streams_, num_output_streams_);
+}
+
+}  // namespace content