[ios] Adds a provider API for AudioSessionController.

ios/public/provider/chrome/browser/voice/test_voice_search_provider.mm

+// 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.
+
+#import "ios/public/provider/chrome/browser/voice/test_voice_search_provider.h"
+
+#include "base/mac/scoped_nsobject.h"
+#import "ios/public/provider/chrome/browser/voice/voice_search_language.h"
+
+TestVoiceSearchProvider::TestVoiceSearchProvider() {}
+
+TestVoiceSearchProvider::~TestVoiceSearchProvider() {}
+
+NSArray* TestVoiceSearchProvider::GetAvailableLanguages() const {
+  base::scoped_nsobject<VoiceSearchLanguage> en([[VoiceSearchLanguage alloc]
+          initWithIdentifier:@"en-US"
+                 displayName:@"English (US)"
+      localizationPreference:nil]);
+  return @[ en ];
+}
+
+AudioSessionController* TestVoiceSearchProvider::GetAudioSessionController()
+    const {
+  // TODO(rohitrao): Return a TestAudioSessionController once the class with the
+  // same name is removed from the internal tree.
+  return nullptr;
+}