Pass shared_ptr<> arguments by const reference

These arguments are not expensive to copy. However, it makes sense to
pass such pointers by const reference when they are just intended for
reading.

Some reading about this issue is here:
https://www.internalpointers.com/post/move-smart-pointers-and-out-functions-modern-c

Fixes some Coverity scan defects.

src/TocBuilder.cpp

@@ -24,7 +24,7 @@ namespace lyx {
 
 
 
-TocBuilder::TocBuilder(shared_ptr<Toc> toc)
+TocBuilder::TocBuilder(shared_ptr<Toc> const & toc)
 	: toc_(toc ? toc : make_shared<Toc>()),
 	  stack_()
 {

src/TocBuilder.h

@@ -27,7 +27,7 @@ class DocIterator;
 class TocBuilder
 {
 public:
-	TocBuilder(std::shared_ptr<Toc> toc);
+	TocBuilder(std::shared_ptr<Toc> const & toc);
 	/// Open a level.
 	/// When entering a float or flex or paragraph (with AddToToc)
 	void pushItem(DocIterator const & dit, docstring const & s,

src/frontends/qt/Action.cpp

@@ -40,7 +40,7 @@ Action::Action(FuncRequest func, QIcon const & icon, QString const & text,
 }
 
 
-Action::Action(shared_ptr<FuncRequest const> func,
+Action::Action(shared_ptr<FuncRequest const> const & func,
                QIcon const & icon, QString const & text,
                QString const & tooltip, QObject * parent)
 	: QAction(parent), func_(func), icon_(icon)

src/frontends/qt/Action.h

@@ -39,7 +39,7 @@ public:
 
 	// Takes shared ownership of func.
 	// Use for perf-sensitive code such as populating menus.
-	Action(std::shared_ptr<FuncRequest const> func,
+	Action(std::shared_ptr<FuncRequest const> const & func,
 	       QIcon const & icon, QString const & text,
 	       QString const & tooltip, QObject * parent);
 

src/frontends/qt/TocModel.cpp

@@ -160,7 +160,7 @@ void TocModel::updateItem(DocIterator const & dit)
 }
 
 
-void TocModel::reset(shared_ptr<Toc const> toc)
+void TocModel::reset(shared_ptr<Toc const> const & toc)
 {
 	toc_ = toc;
 	if (toc_->empty()) {

src/frontends/qt/TocModel.h

@@ -39,7 +39,7 @@ public:
 	///
 	TocModel(QObject * parent);
 	///
-	void reset(std::shared_ptr<Toc const>);
+	void reset(std::shared_ptr<Toc const> const &);
 	///
 	void reset();
 	///

src/support/FileMonitor.cpp

@@ -158,7 +158,7 @@ void FileMonitorGuard::notifyChange(QString const & path)
 }
 
 
-FileMonitor::FileMonitor(std::shared_ptr<FileMonitorGuard> monitor)
+FileMonitor::FileMonitor(std::shared_ptr<FileMonitorGuard> const & monitor)
 	: monitor_(monitor)
 {
 	connectToFileMonitorGuard();
@@ -193,7 +193,7 @@ void FileMonitor::changed(bool const exists)
 }
 
 
-ActiveFileMonitor::ActiveFileMonitor(std::shared_ptr<FileMonitorGuard> monitor,
+ActiveFileMonitor::ActiveFileMonitor(std::shared_ptr<FileMonitorGuard> const & monitor,
                                      FileName const & filename, int interval)
 	: FileMonitor(monitor), filename_(filename), interval_(interval),
 	  timestamp_(0), checksum_(0), cooldown_(true)

src/support/FileMonitor.h

@@ -128,7 +128,7 @@ class FileMonitor : public QObject
 	Q_OBJECT
 
 public:
-	FileMonitor(std::shared_ptr<FileMonitorGuard> monitor);
+	FileMonitor(std::shared_ptr<FileMonitorGuard> const & monitor);
 
 	typedef signal<void(bool)> sig;
 	typedef sig::slot_type slot;
@@ -166,7 +166,7 @@ class ActiveFileMonitor : public FileMonitor
 {
 	Q_OBJECT
 public:
-	ActiveFileMonitor(std::shared_ptr<FileMonitorGuard> monitor,
+	ActiveFileMonitor(std::shared_ptr<FileMonitorGuard> const & monitor,
 	                  FileName const & filename, int interval);
 	/// call checkModified asynchronously
 	void checkModifiedAsync();