Fix GET /sessions issue if there is at least 1 session in W3C mode.

The issue is that session->capabilities is not available W3C mode since
it was moved to 'body' object when session is initiated. Therefore, when
GET /sessions is called, session->capabilities will trigger errors.

Bug: chromedriver:2798
Change-Id: Ifc7dbc69d00485a53a150a96a7b6c94b9578bdb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504760Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Long Ly <loly@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#638198}

chrome/test/chromedriver/session_commands.cc

@@ -327,8 +327,11 @@ Status InitSessionHelper(const InitSessionParams& bound_params,
       CreateCapabilities(session, capabilities, *desired_caps);
 
   if (session->w3c_compliant) {
+    std::unique_ptr<base::DictionaryValue> capabilities =
+        std::unique_ptr<base::DictionaryValue>(
+            session->capabilities->DeepCopy());
     base::DictionaryValue body;
-    body.SetDictionary("capabilities", std::move(session->capabilities));
+    body.SetDictionary("capabilities", std::move(capabilities));
     body.SetString("sessionId", session->id);
     value->reset(body.DeepCopy());
   } else {