Use mojo from the PDF extension instead of using an extension API.

extensions/renderer/resources/mime_handler_private_custom_bindings.js

-// Copyright 2015 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 bindings for the mime handler API.
- */
-
-var binding = require('binding').Binding.create('mimeHandlerPrivate');
-
-var NO_STREAM_ERROR =
-    'Streams are only available from a mime handler view guest.';
-var STREAM_ABORTED_ERROR = 'Stream has been aborted.';
-
-var servicePromise = Promise.all([
-    requireAsync('content/public/renderer/frame_interfaces'),
-    requireAsync('extensions/common/api/mime_handler.mojom'),
-    requireAsync('mojo/public/js/router'),
-]).then(function(modules) {
-  var frameInterfaces = modules[0];
-  var mojom = modules[1];
-  var routerModule = modules[2];
-  return new mojom.MimeHandlerService.proxyClass(new routerModule.Router(
-      frameInterfaces.getInterface(mojom.MimeHandlerService.name)));
-});
-
-// Stores a promise to the GetStreamInfo() result to avoid making additional
-// calls in response to getStreamInfo() calls.
-var streamInfoPromise;
-
-function throwNoStreamError() {
-  throw new Error(NO_STREAM_ERROR);
-}
-
-function createStreamInfoPromise() {
-  return servicePromise.then(function(service) {
-    return service.getStreamInfo();
-  }).then(function(result) {
-    if (!result.stream_info)
-      throw new Error(STREAM_ABORTED_ERROR);
-    return result.stream_info;
-  }, throwNoStreamError);
-}
-
-function constructStreamInfoDict(streamInfo) {
-  var headers = {};
-  for (var header of streamInfo.response_headers) {
-    headers[header[0]] = header[1];
-  }
-  return {
-    mimeType: streamInfo.mime_type,
-    originalUrl: streamInfo.original_url,
-    streamUrl: streamInfo.stream_url,
-    tabId: streamInfo.tab_id,
-    embedded: !!streamInfo.embedded,
-    responseHeaders: headers,
-  };
-}
-
-binding.registerCustomHook(function(bindingsAPI) {
-  var apiFunctions = bindingsAPI.apiFunctions;
-  apiFunctions.setHandleRequestWithPromise('getStreamInfo', function() {
-    if (!streamInfoPromise)
-      streamInfoPromise = createStreamInfoPromise();
-    return streamInfoPromise.then(constructStreamInfoDict);
-  });
-
-  apiFunctions.setHandleRequestWithPromise('abortStream', function() {
-    return servicePromise.then(function(service) {
-      return service.abortStream().then(function() {});
-    }).catch(throwNoStreamError);
-  });
-});
-
-exports.$set('binding', binding.generate());