app_shell: Initial skeleton of a GCD target device setup API

extensions/shell/common/api/shell_gcd.idl

+// Copyright 2014 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.
+
+// Setup related functions for a Google Cloud Devices (GCD) target device
+// running on Chrome OS Core. The actual bootstrapping and GCD registration is
+// handled by the privetd and buffet system daemons.
+namespace shell.gcd {
+
+  enum BootstrapStatus {
+    // Attempting to bootstrap onto Wi-Fi network.
+    bootstrapping,

[Ken Rockot(use gerrit already), 2014/10/30 22:01:05]

The naming is fine in general. All I really meant by "overloaded" is that you
have "bootstrap" referring to the overall bootstrap process, which is complete
when BootstrapStatus is "completed."

But then you also have "connection" being documented as "has bootstrapped",
meaning that the subprocess of wifi bootstrapping has completed.

This is confusing to me. I don't think it's necessary to change
BootstrapStatus/getBootstrapStatus names. Probably just a good idea to clarify
the documentation and maybe reconsider the name of this first state's name (my
strawman suggestions are "initializing", "uninitialized", "disconnected", etc.)

Also everything lgtm so far otherwise, if you need a stamp

+    
+    // Has bootstrapped, connecting to Wi-Fi.
+    connecting,
+    
+    // Has connected, registering with GCD backend.
+    registering,
+    
+    // Bootstrap completed.
+    completed
+  };
+  
+  callback BootstrapStatusCallback = void(BootstrapStatus status);
+
+  interface Functions {
+    // Returns the current bootstrap status via |callback|.
+    static void getBootstrapStatus(BootstrapStatusCallback callback);
+  };
+  
+  interface Events {
+    // Notifies that bootstrapping has transitioned to a new |status|.
+    static void onBootstrapStatusChanged(BootstrapStatus status);
+  };
+};