Enable chrome.accessibilityFeatures on stable channel

BUG=378014

Review URL: https://codereview.chromium.org/317013006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275648 0039d316-1c4b-4281-b951-d872f2087c98

chrome/common/extensions/api/_permission_features.json

@@ -21,11 +21,11 @@
 
 {
   "accessibilityFeatures.modify": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["extension", "platform_app"]
   },
   "accessibilityFeatures.read": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["extension", "platform_app"]
   },
   "accessibilityPrivate": {