gpu: Consult scissor for clip bounds

When querying clip bounds, also check the scissor rect, because
sometimes that one is tighter than the clip bounds, because the clip
bounds need to track some larger rounded corners.

Makes a few tests harder to break.

gsk/gpu/gskgpunodeprocessor.c

@@ -531,14 +531,25 @@ static void
 gsk_gpu_node_processor_get_clip_bounds (GskGpuNodeProcessor *self,
                                         graphene_rect_t     *out_bounds)
 {
-  graphene_rect_offset_r (&self->clip.rect.bounds,
-                          - self->offset.x,
-                          - self->offset.y,
-                          out_bounds);
+  graphene_rect_t scissor;
 
-  /* FIXME: We could try the scissor rect here.
-   * But how often is that smaller than the clip bounds?
-   */
+  if (gsk_gpu_node_processor_rect_device_to_clip (self,
+                                                  &GSK_RECT_INIT_CAIRO (&self->scissor),
+                                                  &scissor))
+    {
+      if (!gsk_rect_intersection (&scissor, &self->clip.rect.bounds, out_bounds))
+        {
+          g_warning ("Clipping is broken, everything is clipped, but we didn't early-exit.\n");
+          *out_bounds = self->clip.rect.bounds;
+        }
+    }
+  else
+    {
+      *out_bounds = self->clip.rect.bounds;
+    }
+
+  out_bounds->origin.x -= self->offset.x;
+  out_bounds->origin.y -= self->offset.y;
 }
  
 static gboolean G_GNUC_WARN_UNUSED_RESULT