Use wxBitmapBundle instead of bitmap scale factor in wxGtkImage

Minimal changes to the code to allow using bigger bitmaps from
wxBitmapBundle in high DPI instead of having to create individual
bitmaps with scale factor greater than 1.

Notice that this is not actually used anywhere in wxGTK yet, but will be
soon.

include/wx/gtk/private/image.h

@@ -5,6 +5,9 @@
 // Licence:     wxWindows licence
 ///////////////////////////////////////////////////////////////////////////////
 
+#include "wx/bmpbndl.h"
+#include "wx/math.h"
+
 // Class that can be used in place of GtkImage, to allow drawing of alternate
 // bitmaps, such as HiDPI or disabled.
 
@@ -14,14 +17,26 @@ public:
     struct BitmapProvider
     {
         virtual ~BitmapProvider() { }
+
+        virtual double GetScale() const = 0;
         virtual wxBitmap Get() const = 0;
-        virtual void Set(const wxBitmap&) { }
+        virtual void Set(const wxBitmapBundle&) { }
+
+        // Simple helpers used in implementation.
+        bool IsScaled() const { return !wxIsSameDouble(GetScale(), 1); }
+        wxBitmap GetAtScale(const wxBitmapBundle& b) const
+        {
+            return b.GetBitmap(b.GetDefaultSize()*GetScale());
+        }
     };
 
     static GType Type();
     static GtkWidget* New(BitmapProvider* provider);
     static GtkWidget* New(wxWindow* win = NULL);
-    void Set(const wxBitmap& bitmap);
+
+    // Use bitmaps from the given bundle, the logical bitmap size is the
+    // default size of the bundle.
+    void Set(const wxBitmapBundle& bitmapBundle);
 
     // This pointer is never null and is owned by this class.
     BitmapProvider* m_provider;