Move Mime type handling to streamsPrivate API, so that it works on Desktop Chrome.

chrome/common/extensions/api/_manifest_features.json

 // 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.
 
 {
   "app": {
     "channel": "stable",
     "extension_types": ["packaged_app", "hosted_app", "platform_app"]
   },
   // The default platform app CSP can only be overridden by whitelisted apps.
@@ skipping 163 matching lines @@
     ]
   },
   "key": {
     "channel": "stable",
     "extension_types": "all"
   },
   "manifest_version": {
     "channel": "stable",
     "extension_types": "all"
   },
+  "mime_types": {
+    "channel": "stable",
+    "extension_types": [ "extension", "packaged_app", "platform_app" ],
+    "whitelist": [
+      "oickdpebdnfbgkcaoklfcdhjniefkcji",  // browser_tests
+      "gbkeegbaiigmenfmjfclcdgdpimamgkj",  // QuickOffice
+      "ionpfmkccalenbmnddpbmocokhaknphg"   // QuickOffice Dev
+    ]
+  },
   "minimum_chrome_version": {
     "channel": "stable",
     "extension_types": [
       "extension", "packaged_app", "hosted_app", "platform_app"
     ]
   },
   "nacl_modules": {
     "channel": "stable",
     "extension_types": [
       "extension", "packaged_app", "hosted_app", "platform_app"
@@ skipping 95 matching lines @@
     "channel": "stable",
     "extension_types": "all"
   },
   "web_accessible_resources": {
     "channel": "stable",
     "extension_types": [
       "extension", "packaged_app", "hosted_app"
     ]
   }
 }