Auto merge of servo#2796 - staktrace:dump_request, r=kvark

Don't try to resolve blobs that weren't requested

r? @kvark

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webrender/src/resource_cache.rs

@@ -662,6 +662,7 @@ impl ResourceCache {
                         if let Some(dirty) = dirty_rect {
                             if intersect_for_tile(dirty, actual_size, tile_size, tile_offset).is_none() {
                                 // don't bother requesting unchanged tiles
+                                self.pending_image_requests.remove(&request);
                                 return
                             }
                         }