[ios] Adds a provider API for AudioSessionController.

ios/public/provider/chrome/browser/voice/test_audio_session_controller.h

+// 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 IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_TEST_AUDIO_SESSION_CONTROLLER_H_
+#define IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_TEST_AUDIO_SESSION_CONTROLLER_H_
+
+#include "base/macros.h"
+#include "ios/public/provider/chrome/browser/voice/audio_session_controller.h"
+
+// No-op AudioSessionController for use in tests.
+class TestAudioSessionController : public AudioSessionController {
+ public:
+  TestAudioSessionController() = default;
+  ~TestAudioSessionController() override = default;
+
+  // AudioSessionController:
+  void InitializeSessionIfNecessary() override;
+  AudioSessionMode GetSessionMode() override;
+  void SetSessionMode(AudioSessionMode mode) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TestAudioSessionController);
+};
+
+#endif  // IOS_PUBLIC_PROVIDER_CHROME_BROWSER_VOICE_TEST_AUDIO_SESSION_CONTROLLER_H_