Enable USB device permission for interface class for stable

BUG=629223

Review-Url: https://codereview.chromium.org/2614663005
Cr-Commit-Position: refs/heads/master@{#443504}

chrome/common/extensions/docs/templates/articles/app_usb.html

@@ -42,8 +42,8 @@ Chrome Apps can also connect to <a href="serial">serial</a> and
 </p>
 <p>
   You must declare the VID/PID pairs for each type of device you want to use
-  under the "usbDevices" permission in your app's manifest file, as shown in the
-  example below:</p>
+  under the <code>usbDevices</code> permission in your app's manifest file, as
+  shown in the example below:</p>
 
 <pre data-filename="manifest.json">
 "permissions": [
@@ -61,6 +61,56 @@ Chrome Apps can also connect to <a href="serial">serial</a> and
 <p class="note">Note that only decimal numbers are allowed in JSON format.
   You cannot use hexadecimal numbers in these fields.</p>
 
+<p>Since <b>Chrome 57</b>, the requirement for declaring all the device types
+  in the app manifest is relaxed for apps running as Chrome OS
+  <a href="apps/manifest/kiosk_enabled">kiosk apps</a>.
+  For kiosk apps, you can use the <code>interfaceClass</code> permission
+  property to request permission to access USB devices that:
+  <ul>
+    <li>implement a USB interface of a specific interface class</li>
+    <li>have a specific USB device class</li>
+  </ul>
+  For example, the following <code>usbDevices</code> permission would grant an
+  app access to all USB devices that implement a printer interface (interface
+  class code 7), and to USB hub devices (device class code 9):</p>
+
+<pre data-filename="manifest.json">
+"permissions": [
+  {
+    "usbDevices": [
+      {"interfaceClass": 7},
+      {"interfaceClass": 9}
+    ]
+  }
+]
+</pre>
+
+<p>For the list of acceptable <code>interfaceClass</code> values, see
+  <a href="http://www.usb.org/developers/defined_class">USB Class Codes</a>.
+  </p>
+
+<p>The <code>interfaceClass</code> property can be combined with the
+  <code>vendorId</code> property to get access only to USB devices from a
+  specific vendor, as demonstrated by the following example:</p>
+
+<pre data-filename="manifest.json">
+"permissions": [
+  {
+    "usbDevices": [
+      {
+        "vendorId": 123,
+        "interfaceClass": 7
+      }
+    ]
+  }
+]
+</pre>
+
+<p class="note">Note that <code>usbDevices</code> permissions with
+  <code>interfaceClass</code> property have effect only when the app is running
+  in kiosk session - outside a kiosk session these permissions will be ignored.
+  </p>
+
 <h2 id="finding_device">Finding a device</h2>
 
 <p>

extensions/common/api/_behavior_features.json

@@ -43,7 +43,7 @@
     ]
   },
   "allow_usb_devices_permission_interface_class": {
-    "channel": "dev",
+    "channel": "stable",
     "extension_types": ["platform_app"],
     "session_types": ["kiosk"] 
   },