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, 2 insertions, 2 deletions

diff --git a/src/widget/wsingletoncontainer.h b/src/widget/wsingletoncontainer.h
index 87812d4f94..168e263ad4 100644
--- a/src/widget/wsingletoncontainer.h
+++ b/src/widget/wsingletoncontainer.h
@@ -73,12 +73,12 @@ class SingletonMap {
     // Takes a constructed QWidget and inserts it in the map of available
     // singletons.  Checks that an object of that name hasn't already been
     // defined.
-    void insertSingleton(QString objectName, QWidget* widget);
+    void insertSingleton(const QString& objectName, QWidget* widget);
 
     // We don't want to end up with badly-constructed containers, so only
     // provide a factory function.  Returns NULL if the objectName is not in
     // the map.
-    QWidget* getSingletonWidget(QString objectName) const;
+    QWidget* getSingletonWidget(const QString& objectName) const;
 
   private:
     QMap<QString, QWidget*> m_singletons;