Change confirm IDP login webdriver command to click dialog button (#510)

* Change confirm IDP login webdriver command to click dialog button

* Change confirm IDP login webdriver command to click dialog button

* Remove error API references

* Add commas

* Address npm's comments

spec/index.bs

@@ -1985,9 +1985,9 @@ The [=remote end steps=] are:
 
 1. Return [=success=] with data `null`.
 
-## Confirm IDP login ## {#webdriver-confirmidplogin}
+## Click dialog button ## {#webdriver-clickdialogbutton}
 
-<figure id="table-webdriver-confirmidplogin" class="table">
+<figure id="table-webdriver-clickdialogbutton" class="table">
     <table class="data">
         <thead>
             <tr>
@@ -1998,20 +1998,29 @@ The [=remote end steps=] are:
         <tbody>
             <tr>
                 <td>POST</td>
-                <td>`/session/{session id}/fedcm/confirmidplogin`</td>
+                <td>`/session/{session id}/fedcm/clickdialogbutton`</td>
             </tr>
         </tbody>
     </table>
 </figure>
 
 The [=remote end steps=] are:
 
-1. If no FedCM dialog is currently open, or the dialog is not a [=confirm IDP
-    login dialog=] return a [=error|WebDriver error=] with [=error code=]
-    [=no such alert=].
+1. If |parameters| is not a JSON [[ECMASCRIPT#sec-json-object|Object]], return a
+   [=error|WebDriver error=] with [=error code=] [=invalid argument=].
+
+1. Let |dialogButton| be the result of [=getting a property=] named
+   `"dialogButton"` from |parameters|.
+
+1. If |dialogButton| is not a string that is "`ConfirmIdpLoginContinue`", return
+   a [=error|WebDriver error=] with [=error code=] [=invalid argument=].
+
+1. If no FedCM dialog is currently open or the dialog is not a [=confirm IDP
+   login dialog=], return a [=error|WebDriver error=] with [=error code=] [=no
+   such alert=].
 
-1. Act as if the user had clicked the "continue" button in the dialog and
-    initiate the login flow.
+1. Act as if the user had clicked the "continue" button in the [=confirm IDP
+   login dialog=] and initiate the login flow.
 
 1. Return [=success=] with data `null`.