Added a private chromeAuthPrivate API.

chrome/common/extensions/api/extension_api.json

 [
   {
     "namespace": "extension",
     "unprivileged": true,
     "types": [
       {
         "id": "MessageSender",
         "type": "object",
         "description": "An object containing information about the script context that sent a message or request.",
         "properties": {
@@ skipping 6152 matching lines @@
         "description": "Fired when browser terminates debugging session for the tab.",
         "parameters": [
           {
             "type": "integer",
             "name": "tabId",
             "description": "The id of the tab that was detached."
           }
         ]
       }
     ]
+  },
+  {
+    "namespace": "chromeAuthPrivate",
+    "nodoc": "true",
+    "functions": [
+      {
+        "name": "setCloudPrintCredentials",
+        "description": "Sets the login credentials for Cloud Print.",
+        "type": "function",
+        "parameters": [
+          {
+            "name": "userEmail",
+            "type": "string",
+            "description": "The email address of the user."
+          },
+          {
+            "name": "robotEmail",
+            "type": "string",
+            "description": "The email address of the robot account."
+          },
+          {
+            "name": "credentials",
+            "type": "string",
+            "description": "The login credentials(OAuth2 Auth code)."
+          },
+          {
+            "name": "callback",
+            "type": "function",
+            "description": "Called when a failure happens. Called upon success only in tests.",
+            "optional": "true",
+            "parameters": [
+              {
+                "name": "result",
+                "type": "string",
+                "description": "A string result code. The value is non-empty on success only in tests.",
+                "optional": "true"
+              }
+            ]
+          }
+        ]
+      }
+    ]
   }
 ]