Make interface between wxGridHeaderCtrl and wxGrid more explicit

Rename the functions used from wxGridHeaderCtrl event handlers to start
with DoHeader prefix to make it clear that they're (only) used by it in
an attempt to make things more clear and more uniform.

No real changes.

include/wx/generic/grid.h

@@ -2534,18 +2534,26 @@ private:
 
     void DoColHeaderClick(int col);
 
-    void DoStartResizeCol(int col);
-    void DoUpdateResizeColWidth(int w);
     void DoStartMoveCol(int col);
 
     void DoEndDragResizeRow(const wxMouseEvent& event, wxGridWindow *gridWindow);
     void DoEndDragResizeCol(const wxMouseEvent& event, wxGridWindow *gridWindow);
-    void DoEndDragResizeCol(const wxMouseEvent& event)
-    {
-        DoEndDragResizeCol(event, m_gridWin);
-    }
     void DoEndMoveCol(int pos);
 
+    // Helper function returning the position (only the horizontal component
+    // really counts) corresponding to the given column drag-resize event.
+    //
+    // It's a bit ugly to create a phantom mouse position when we really only
+    // need the column width anyhow, but wxGrid code was originally written to
+    // expect the position and not the width and it's simpler to keep it happy
+    // by giving it the position than to change it.
+    wxPoint GetPositionForResizeEvent(int width) const;
+
+    // functions called by wxGridHeaderCtrl while resizing m_dragRowOrCol
+    void DoHeaderStartDragResizeCol(int col);
+    void DoHeaderDragResizeCol(int width);
+    void DoHeaderEndDragResizeCol(int width);
+
     // process a TAB keypress
     void DoGridProcessTab(wxKeyboardState& kbdState);