Add the IDL and stub implementation for the chrome.autofillPrivate API.

chrome/common/extensions/api/_permission_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.
 
 // This features file defines permissions for extension APIs implemented
 // under src/chrome.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 
 // To add a new whitelisted ID, SHA-1 it and force it to uppercase. In Bash:
@@ skipping 48 matching lines @@
       "extension_types": ["extension", "platform_app"],
       "whitelist": [
         "05EBA3051DFCA6AF17070AEE5FE8C66322FF4738",  // http://crbug.com/431978
         "11B478CEC461C766A2DC1E5BEEB7970AE06DC9C2",  // http://crbug.com/458218
         "0EFB879311E9EFBB7C45251F89EC655711B1F6ED",  // http://crbug.com/458218
         "9193D3A51E2FE33B496CDA53EA330423166E7F02",  // http://crbug.com/458218
         "F9119B8B18C7C82B51E7BC6FF816B694F2EC3E89"   // http://crbug.com/458218
       ]
     }
   ],
+  "autofillPrivate": {
+    "channel": "trunk",
+    "extension_types": ["extension", "platform_app"],
+    "location": "component"
+  },
   "autotestPrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app"],
     "location": "component"
   },
   "background": {
     "channel": "stable",
     "extension_types": [
       "platform_app", "extension", "legacy_packaged_app", "hosted_app"
     ]
@@ skipping 913 matching lines @@
   },
   "webstorePrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "hosted_app"],
     "whitelist": [
       "B44D08FD98F1523ED5837D78D0A606EA9D6206E5",  // Web Store
       "2653F6F6C39BC6EEBD36A09AFB92A19782FF7EB4"   // Enterprise Web Store
     ]
   }
 }