Bug 1580922 - changing the blob visible area can require rasterization requests. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D47084

--HG--
extra : moz-landing-system : lando

gfx/wr/webrender/src/render_backend.rs

@@ -1692,6 +1692,9 @@ fn get_blob_image_updates(updates: &[ResourceUpdate]) -> Vec<BlobImageKey> {
             ResourceUpdate::UpdateBlobImage(ref img) => {
                 requests.push(img.key);
             }
+            ResourceUpdate::SetBlobImageVisibleArea(key, ..) => {
+                requests.push(key);
+            }
             _ => {}
         }
     }