Don't start speech synthesis until after the audio mixer is initialized.

chrome/browser/extensions/extension_tts_api_chromeos.h

+// Copyright (c) 2011 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_CHROMEOS_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_CHROMEOS_H_
+#pragma once
+
+// This is called by AudioMixerAlsa to signal that it's safe to begin
+// using TTS on ChromeOS - this must happen after AudioMixerAlsa has
+// finished its initialization. NotificationService would be cleaner,
+// but it's not available at the point when this code needs to be called.
+void EnableChromeOsTts();
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_TTS_API_CHROMEOS_H_