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

chrome/common/extensions/api/webstore_private.json

Index: chrome/common/extensions/api/webstore_private.json
diff --git a/chrome/common/extensions/api/webstore_private.json b/chrome/common/extensions/api/webstore_private.json
index f80ff335a23e978ebebc00a3e49ac60e043a2be2..201815e8ae29df3ecf811dbf083e2847df6bb0a9 100644
--- a/chrome/common/extensions/api/webstore_private.json
+++ b/chrome/common/extensions/api/webstore_private.json
@@ -252,6 +252,18 @@
             ]
           }
         ]
+      },
+      {
+        "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"
+          }
+        ]
       }
     ]
   }