Pass non-trivial/large function args by reference

Fixes a bunch of `-Wclazy-function-args-by-ref` warnings. See
https://github.com/KDE/clazy/blob/master/docs/checks/README-function-args-by-ref.md
for details.

Most of these changes are automated, using the clazy fixit by setting
the `CLAZY_EXPORT_FIXES` before compilation and then running:

    $ mkdir /tmp/patch
    $ find ../src -iname "*.yaml" -exec mv {} /tmp/patch \;
    $ clang-apply-replacements /tmp/patch

1 files changed, 3 insertions, 4 deletions

diff --git a/src/errordialoghandler.h b/src/errordialoghandler.h
index 6bd26bddd8..285546b079 100644
--- a/src/errordialoghandler.h
+++ b/src/errordialoghandler.h
@@ -152,8 +152,7 @@ class ErrorDialogHandler : public QObject {
     // requested message box. They return false if a dialog with the same key
     // (or title if no key) is already displayed. If shouldQuit is true, Mixxx
     // will shut down.
-    bool requestErrorDialog(DialogType type, QString message,
-                            bool shouldQuit = false);
+    bool requestErrorDialog(DialogType type, const QString& message, bool shouldQuit = false);
     bool requestErrorDialog(ErrorDialogProperties* props);
 
     // Allows a means for main() to skip exec() if there was a critical or fatal
@@ -162,12 +161,12 @@ class ErrorDialogHandler : public QObject {
 
   signals:
     void showErrorDialog(ErrorDialogProperties* props);
-    void stdButtonClicked(QString key, QMessageBox::StandardButton whichStdButton);
+    void stdButtonClicked(const QString& key, QMessageBox::StandardButton whichStdButton);
 
   private slots:
     /** Actually displays the box */
     void errorDialog(ErrorDialogProperties* props);
-    void boxClosed(QString key, QMessageBox* msgBox);
+    void boxClosed(const QString& key, QMessageBox* msgBox);
 
   private:
     // Private constructor