Add AudioStreamRegistry. Move stream counting logic

content/test/mock_audio_stream_registry.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_RENDERER_HOST_MEDIA_MOCK_AUDIO_STREAM_REGISTRY_H_
+#define CONTENT_BROWSER_RENDERER_HOST_MEDIA_MOCK_AUDIO_STREAM_REGISTRY_H_
+
+#include "content/test/mock_audio_stream_registry.h"
+
+#include "testing/gmock/include/gmock/gmock.h"
+
+namespace content {
+
+MockAudioStreamRegistry::MockAudioStreamRegistry(int render_process_id)
+    : impl_(render_process_id) {
+  // AudioStreamRegistryImpl has many DCHECKs. We reuse them here by
+  // forwarding all calls.
+  ON_CALL(*this, RegisterOutputStream(testing::_))
+      .WillByDefault(
+          testing::Invoke(&impl_, &AudioStreamRegistry::RegisterOutputStream));
+  ON_CALL(*this, DeregisterOutputStream(testing::_))
+      .WillByDefault(testing::Invoke(
+          &impl_, &AudioStreamRegistry::DeregisterOutputStream));
+  ON_CALL(*this, OutputStreamStateChanged(testing::_, testing::_))
+      .WillByDefault(testing::Invoke(
+          &impl_, &AudioStreamRegistry::OutputStreamStateChanged));
+}
+
+MockAudioStreamRegistry::~MockAudioStreamRegistry() {}
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_RENDERER_HOST_MEDIA_MOCK_AUDIO_STREAM_REGISTRY_H_