Export a private webstore API to call into the new inline sign-in flow.

chrome/common/extensions/api/webstore_private.json

 // Copyright (c) 2012 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.
 
 [
   {
     "namespace":"webstorePrivate",
     "description": "none",
     "functions": [
       {
@@ skipping 234 matching lines @@
         "parameters": [
           {
             "name": "callback",
             "type": "function",
             "optional": "false",
             "parameters": [
               { "name": "is_incognito", "type": "boolean" }
             ]
           }
         ]
+      },
+      {
+        "name": "signIn",
+        "description": "Signs the user into Chrome.",
+        "parameters": [
+          {
+            "name": "continue_url",
+            "type": "string",
+            "description": "The continue URL to navigate to once sign-in completes.",

[guohui, 2014/03/12 18:18:59]

you are probably still working on it, but i think the function needs at least
one input param for the continue url and one input param for the callback to
notify webstore of the result.

+            "optional": "false"
+          }
+        ]
       }
     ]
   }
 ]