Declare wxPG_DEFAULT_IMAGE_SIZE as wxDefaultSize constant.

wxDefaultSize is an equivalent of wxSize(-1,-1) but is more portable.

include/wx/propgrid/property.h

@@ -1293,7 +1293,7 @@ public:
         @remarks
         - Default behaviour is to return wxSize(0,0), which means no image.
         - Default image width or height is indicated with dimension -1.
-        - You can also return wxPG_DEFAULT_IMAGE_SIZE, i.e. wxSize(-1, -1).
+        - You can also return wxPG_DEFAULT_IMAGE_SIZE, i.e. wxDefaultSize.
     */
     virtual wxSize OnMeasureImage( int item = -1 ) const;
 

include/wx/propgrid/propgriddefs.h

@@ -246,7 +246,7 @@ class wxPGValidationInfo;
 /** If property is supposed to have custom-painted image, then returning
     this in OnMeasureImage() will usually be enough.
 */
-#define wxPG_DEFAULT_IMAGE_SIZE             wxSize(-1, -1)
+#define wxPG_DEFAULT_IMAGE_SIZE  wxDefaultSize
 
 
 /** This callback function is used for sorting properties.