Added CanApplyParentThemeBackground and use it in wxMSW's

wxNotebook::ApplyThemeBackground.  It's in the common base classes so
that someday it's usage can expand to the other platforms as well.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26085 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/window.h

@@ -394,6 +394,13 @@ public:
     virtual void SetThemeEnabled(bool enableTheme) { m_themeEnabled = enableTheme; }
     virtual bool GetThemeEnabled() const { return m_themeEnabled; }
 
+        // Returns true if this class should have the background colour
+        // changed to match the parent window's theme.  For example when a
+        // page is added to a notebook it and it's children may need to have
+        // the colours adjusted depending on the current theme settings, but
+        // not all windows/controls can do this without looking wrong.
+    virtual bool CanApplyParentThemeBackground() const { return false; }
+    
         // returns true if this window should inherit its parent colours on
         // creation
     virtual bool ShouldInheritColours() const { return false; }