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

extensions/common/api/_api_features.json

 // Copyright 2014 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.
 
 // This features file defines extension APIs implemented under src/extensions.
 // See chrome/common/extensions/api/_features.md to understand this file, as
 // well as feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 212 matching lines @@
   "management.getSelf": {
     "dependencies": [],
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
   },
   "management.uninstallSelf": {
     "dependencies": [],
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "platform_app"]
   },
-  "mimeHandlerPrivate": {
-    "dependencies": ["manifest:mime_types_handler"],
-    "contexts": ["blessed_extension"]
-  },
-  "mojoPrivate": {
+  "mojoPrivate": [{
     "contexts": ["blessed_extension"],
     "channel": "stable",
     "extension_types": ["platform_app", "extension"],
     "whitelist": [
       "226CF815E39A363090A1E547D53063472B8279FA",  // http://crbug.com/574889
       "C17CD9E6868D7B9C67926E0EC612EA25C768418F",  // http://crbug.com/448569
       "A45DABDB47A31CC812E5490AB748C7D05E2D32E9",
       "BFEE2E3B80BE21A645E63E9346DFC383E7CB3BDA",
       "63ED55E43214C211F82122ED56407FF1A807F2A3"
     ]
-  },
+  }, {
+    "dependencies": ["manifest:mime_types_handler"],
+    "contexts": ["blessed_extension"]
+  }],
   "networking.config": {
     "dependencies": ["permission:networking.config"],
     "contexts": ["blessed_extension"]
   },
   "networkingPrivate": [{
     "dependencies": ["permission:networkingPrivate"],
     "contexts": ["blessed_extension"]
   }, {
     "channel": "stable",
     "contexts": ["webui"],
@@ skipping 208 matching lines @@
   }, {
     "channel": "stable",
     "contexts": ["webui"],
     "matches": [
       "chrome://chrome-signin/*",
       "chrome://media-router/*",
       "chrome://oobe/*"
     ]
   }]
 }