Make API chrome.wallpaper.setWallpaper exposed on stable channel.

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 934 matching lines @@
     "platforms": ["chromeos"],
     "whitelist": [
       "3F50C3A83839D9C76334BCE81CDEC06174F266AF",  // System-level virtual kbd
       "06BE211D5F014BAB34BC22D9DDA09C63A81D828E",  // Official XKB virtual kbd
       "CFBF7EE448FA48960FFDA7CEB30F7A21B26AA981",  // Official m17n virtual kbd
       "F94EE6AB36D6C6588670B2B01EB65212D9C64E33",  // Public XKB virtual kbd
       "3E03D9B67FDD31B2438D1CF5070573415DCB3CBA"  // Public m17n virtual kbd
     ]
   },
   "wallpaper": {
-    "channel": "dev",
-    "extension_types": ["platform_app"],
+    "channel": "stable",
+    "extension_types": ["platform_app", "extension"],
     "platforms": ["chromeos"]
   },
   "wallpaperPrivate": {
     "channel": "stable",
     "extension_types": ["platform_app"],
     "location": "component",
     "platforms": ["chromeos"]
   },
   "webNavigation": {
     "channel": "stable",
@@ skipping 24 matching lines @@
   "webstorePrivate": {
     "channel": "stable",
     "extension_types": ["extension", "legacy_packaged_app", "hosted_app"],
     "whitelist": [
       "B44D08FD98F1523ED5837D78D0A606EA9D6206E5",  // Web Store
       "2653F6F6C39BC6EEBD36A09AFB92A19782FF7EB4",  // Enterprise Web Store
       "2779FA8B45841D61A37207CCFAC9CB393964FE5B"   // Login Proxy (prototype)
     ]
   }
 }