[core] Make the BackgroundScheduler a singleton

- Do not carry it over everywhere as parameter, it is a shared
  instance anyway and the lifecycle is pretty much the app lifecycle
  from the moment we instantiate a map.
- Rename to BackgroundScheduler because it is a Scheduler that will
  do tasks in the background, we don't make assumptions if it is a
  thread pool or a single thread.
- Most importantly, remove the dependency from `core` on `platform`.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/mbgl/tile/raster_tile.cpp b/src/mbgl/tile/raster_tile.cpp
index ff02301021..9da11b3595 100644
--- a/src/mbgl/tile/raster_tile.cpp
+++ b/src/mbgl/tile/raster_tile.cpp
@@ -1,4 +1,5 @@
 #include <mbgl/tile/raster_tile.hpp>
+
 #include <mbgl/tile/raster_tile_worker.hpp>
 #include <mbgl/tile/tile_observer.hpp>
 #include <mbgl/tile/tile_loader_impl.hpp>
@@ -17,7 +18,7 @@ RasterTile::RasterTile(const OverscaledTileID& id_,
     : Tile(Kind::Raster, id_),
       loader(*this, id_, parameters, tileset),
       mailbox(std::make_shared<Mailbox>(*Scheduler::GetCurrent())),
-      worker(parameters.workerScheduler,
+      worker(Scheduler::GetBackground(),
              ActorRef<RasterTile>(*this, mailbox)) {
 }