remote-debugging-port for guest sessions.

--remote-debugging-port flag is lost when guest sessions are started on
chromeos.

BUG=None

Review-Url: https://codereview.chromium.org/2141303003
Cr-Commit-Position: refs/heads/master@{#405633}

chrome/browser/chromeos/login/chrome_restart_request.cc

@@ -139,6 +139,7 @@ void DeriveCommandLine(const GURL& start_url,
     ::switches::kPpapiFlashPath,
     ::switches::kPpapiFlashVersion,
     ::switches::kPpapiInProcess,
+    ::switches::kRemoteDebuggingPort,
     ::switches::kRendererStartupDialog,
     ::switches::kRootLayerScrolls,
     ::switches::kEnableShareGroupAsyncTextureUpload,