macos: move setNeedsDisplay helper to GdkMacosCairoView

This isn't needed in the base class, which will eventually get a GL subclass.

gdk/macos/GdkMacosBaseView.c

@@ -57,12 +57,6 @@
   return self;
 }
 
--(void)setNeedsDisplay:(BOOL)needsDisplay
-{
-  for (id child in [self subviews])
-    [child setNeedsDisplay:needsDisplay];
-}
-
 -(void)setOpaqueRegion:(cairo_region_t *)region
 {
   /* Do nothing */

gdk/macos/GdkMacosCairoView.c

@@ -53,6 +53,12 @@
   return YES;
 }
 
+-(void)setNeedsDisplay:(BOOL)needsDisplay
+{
+  for (id child in [self subviews])
+    [child setNeedsDisplay:needsDisplay];
+}
+
 -(void)setCairoSurface:(cairo_surface_t *)cairoSurface
             withDamage:(cairo_region_t *)cairoRegion
 {