Declarative Net Request: Enable the API on dev channel.

BUG=696822

Change-Id: I77b3ed6aba80cf1c41e27148b560fbe7094fb19e
Reviewed-on: https://chromium-review.googlesource.com/1222158Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595618}

extensions/common/api/_manifest_features.json

@@ -111,7 +111,7 @@
     "extension_types": "all"
   },
   "declarative_net_request": {
-    "channel": "trunk",
+    "channel": "dev",
     "extension_types": ["extension"],
     "min_manifest_version": 2
   },

extensions/common/api/_permission_features.json

@@ -190,7 +190,7 @@
     "platforms": ["chromeos"]
   },
   "declarativeNetRequest": {
-    "channel": "trunk",
+    "channel": "dev",
     "extension_types": ["extension"],
     "min_manifest_version": 2
   },