Bug 1433958 - Change code that sets nsIURI.userPass to use nsIURIMutator r=mayhemer

* Code in XMLHttpRequestMainThread is converted to set the username and password individually. This is because when the parameters are empty, it ended up calling SetUserPass(":") which always returns an error.

MozReview-Commit-ID: 3cK5HeyzjFE

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -40,6 +40,7 @@
 #include "nsReadableUtils.h"
 
 #include "nsIURI.h"
+#include "nsIURIMutator.h"
 #include "nsILoadGroup.h"
 #include "nsNetUtil.h"
 #include "nsStringStream.h"
@@ -1483,15 +1484,12 @@ XMLHttpRequestMainThread::Open(const nsACString& aMethod,
   nsAutoCString host;
   parsedURL->GetHost(host);
   if (!host.IsEmpty()) {
-    nsAutoCString userpass;
-    if (!aUsername.IsVoid()) {
-      CopyUTF16toUTF8(aUsername, userpass);
+    if (!aUsername.IsVoid() || !aPassword.IsVoid()) {
+      Unused << NS_MutateURI(parsedURL)
+                  .SetUsername(NS_ConvertUTF16toUTF8(aUsername))
+                  .SetPassword(NS_ConvertUTF16toUTF8(aPassword))
+                  .Finalize(parsedURL);
     }
-    userpass.AppendLiteral(":");
-    if (!aPassword.IsVoid()) {
-      AppendUTF16toUTF8(aPassword, userpass);
-    }
-    parsedURL->SetUserPass(userpass);
   }
 
   // Step 9