Add documentation for enterprise.networkingAttributes API

The new API is only available to force-installed (see intro) extensions
running on Chrome OS.

Bug: 1081333
Change-Id: I5388e0d7e9af1150415226a11c4152d2196bb9f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250001
Auto-Submit: Alexander Hendrich <hendrich@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780327}

chrome/common/extensions/api/enterprise_networking_attributes.idl

@@ -9,7 +9,7 @@
 [platforms = ("chromeos"),
  implemented_in = "chrome/browser/extensions/api/enterprise_networking_attributes/enterprise_networking_attributes_api.h"]
 namespace enterprise.networkingAttributes {
-  dictionary NetworkDetails {
+  [noinline_doc] dictionary NetworkDetails {
     // The device's MAC address.
     DOMString macAddress;
 

chrome/common/extensions/docs/templates/intros/enterprise_networkingAttributes.html

+<p class="note">
+  <strong>Note: </strong>
+  This API is only for
+  <a href="https://support.google.com/chrome/a/answer/1375694?hl=en">extensions pre-installed by policy</a>.
+</p>

chrome/common/extensions/docs/templates/public/extensions/enterprise_networkingAttributes.html

+{{+partials.standard_extensions_api api:apis.extensions.enterprise_networkingAttributes intro:intros.enterprise_networkingAttributes chrome_os_only:true/}}