Remove virtual inheritance from the codebase, refs 6b51d71c85, e21ebb37f5 e326ebae46.

Remove workaround in 3d07327837 / D2136, the pointer from IGUIObject to
IGUITextOwner that avoided the dynamic_cast.
Have the GUIObject implementing class take responsibility of calling the
virtual methods in the base classes.
Leaves the code in a clean state that can serve as an example for new
GUI object classes, such as D1346, refs #4683.

Differential Revision: https://code.wildfiregames.com/D2325
Comments By: Vladislav on IRC 2019-07-30, 2019-08-22, 2019-09-20-23
Tested on: clang 8.0.1, Jenkins

This was SVN commit r23020.

source/gui/CChart.cpp

@@ -32,7 +32,7 @@
 
 CChart::CChart(CGUI& pGUI)
 	: IGUIObject(pGUI),
-	  IGUITextOwner(pGUI),
+	  IGUITextOwner(*static_cast<IGUIObject*>(this)),
 	  m_AxisColor(),
 	  m_AxisWidth(),
 	  m_BufferZone(),
@@ -58,8 +58,17 @@ CChart::~CChart()
 {
 }
 
+void CChart::UpdateCachedSize()
+{
+	IGUIObject::UpdateCachedSize();
+	IGUITextOwner::UpdateCachedSize();
+}
+
 void CChart::HandleMessage(SGUIMessage& Message)
 {
+	IGUIObject::HandleMessage(Message);
+	// IGUITextOwner::HandleMessage(Message); performed in UpdateSeries
+
 	// TODO: implement zoom
 	switch (Message.type)
 	{