Add mime_type_handler key to extension manifests.

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.
 
 // See c/c/e/features/* to understand this file, in particular feature.h,
 // simple_feature.h, and base_feature_provider.h.
 
 {
   "app": {
     "channel": "stable",
@@ skipping 280 matching lines @@
     "extension_types": [ "extension", "legacy_packaged_app", "platform_app" ],
     "whitelist": [
       "oickdpebdnfbgkcaoklfcdhjniefkcji",  // browser_tests
       "gbkeegbaiigmenfmjfclcdgdpimamgkj",  // QuickOffice
       "ionpfmkccalenbmnddpbmocokhaknphg",  // QuickOffice Dev
       "bpmcpldpdmajfigpchkicefoigmkfalc",  // Quickoffice component extension
       "ehibbfinohgbchlgdbfpikodjaojhccn",  // Editor
       "mhjfbmdgcfjbbpaeojofohoefgiehjai"   // PDF
     ]
   },
+  "mime_types_handler": {
+    "channel": "stable",
+    "extension_types": [ "extension", "legacy_packaged_app", "platform_app" ],
+    "whitelist": [
+      "oickdpebdnfbgkcaoklfcdhjniefkcji",  // browser_tests
+      "gbkeegbaiigmenfmjfclcdgdpimamgkj",  // QuickOffice
+      "ionpfmkccalenbmnddpbmocokhaknphg",  // QuickOffice Dev
+      "bpmcpldpdmajfigpchkicefoigmkfalc",  // Quickoffice component extension
+      "ehibbfinohgbchlgdbfpikodjaojhccn",  // Editor
+      "mhjfbmdgcfjbbpaeojofohoefgiehjai"   // PDF
+    ]
+  },
   "minimum_chrome_version": {
     "channel": "stable",
     "extension_types": [
       "extension", "legacy_packaged_app", "hosted_app", "platform_app"
     ]
   },
   "nacl_modules": {
     "channel": "stable",
     "extension_types": [
       "extension", "legacy_packaged_app", "hosted_app", "platform_app"
@@ skipping 143 matching lines @@
       "extension_types": ["platform_app"],
       "location": "component"
     }
   ],
   "webview": {
     "channel": "stable",
     "extension_types": ["platform_app"],
     "min_manifest_version": 2
   }
 }