Add wxRenderer::GetHeaderButtonMargin().

Used for best size calculations of column width.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65947 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/renderer.h

@@ -204,6 +204,8 @@ public:
 
     virtual int GetHeaderButtonHeight(wxWindow *win);
 
+    virtual int GetHeaderButtonMargin(wxWindow *win);
+
     virtual void DrawTreeItemButton(wxWindow *win, wxDC& dc,
                                     const wxRect& rect, int flags = 0);
 
@@ -494,6 +496,14 @@ public:
     */
     virtual int GetHeaderButtonHeight(wxWindow* win) = 0;
 
+    /**
+        Returns the horizontal margin on the left and right sides of header
+        button's label.
+
+        @since 2.9.2
+     */
+    virtual int GetHeaderButtonMargin(wxWindow *win) = 0;
+
     /**
         Get the splitter parameters, see wxSplitterRenderParams.
         The @a win parameter should be a wxSplitterWindow.