chrome/renderer/resources/extensions/tts_engine_custom_bindings.js

// Copyright (c) 2012 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.

// Custom binding for the ttsEngine API.

bindingUtil.registerEventArgumentMassager('ttsEngine.onSpeak',
                                          function(args, dispatch) {
  var text = args[0];
  var options = args[1];
  var requestId = args[2];
  if (args.length !== 3) {
    throw new Error('Unexpected number of args: ' + args.length);
  }

  var sendTtsEvent = function(event) {
    chrome.ttsEngine.sendTtsEvent(requestId, event);
  };
  dispatch([text, options, sendTtsEvent]);
});

let currentRequestId;
bindingUtil.registerEventArgumentMassager(
    'ttsEngine.onSpeakWithAudioStream', function(args, dispatch) {
      let text = args[0];
      let options = args[1];
      let requestId = args[2];
      let audioStreamOptions = args[3];
      if (args.length !== 4) {
        throw new Error('Unexpected number of args: ' + args.length);
      }

      currentRequestId = requestId;

      const sendTtsAudio = function(audioBufferParams) {
        const {audioBuffer, charIndex, isLastBuffer} = audioBufferParams;
        if (currentRequestId == requestId) {
          if (!audioBuffer) {
            throw new Error('Invalid audio buffer: ' + audioBuffer);
          }

          if (audioBuffer.length !== audioStreamOptions.bufferSize) {
            throw new Error(
                `Invalid audio buffer size ` +
                `${audioBuffer.length}; expected == ${
                    audioStreamOptions.length}`);
          }

          chrome.ttsEngine.sendTtsAudio(requestId, {
            audioBuffer,
            charIndex: charIndex !== undefined ? charIndex : -1,
            isLastBuffer: !!isLastBuffer
          });
        }
      };
      dispatch([text, options, audioStreamOptions, sendTtsAudio]);
    });

apiBridge.registerCustomHook(function(api) {
  // Provide a warning if deprecated parameters are used.
  api.apiFunctions.setHandleRequest('updateVoices', function(voices) {
    for (var i = 0; i < voices.length; i++) {
      if (voices[i].gender) {
        console.warn(
            'chrome.ttsEngine.updateVoices: ' +
            'Voice gender is deprecated and values will be ignored ' +
            'starting in Chrome 71.');
        break;
      }
    }
    bindingUtil.sendRequest(
        'ttsEngine.updateVoices', [voices], undefined);
  });
}.bind(this));