[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, 1 insertions, 3 deletions

diff --git a/test/style/style_layer.test.cpp b/test/style/style_layer.test.cpp
index 50aa643b50..5f9de07dba 100644
--- a/test/style/style_layer.test.cpp
+++ b/test/style/style_layer.test.cpp
@@ -18,7 +18,6 @@
 #include <mbgl/style/layers/symbol_layer_impl.hpp>
 #include <mbgl/util/color.hpp>
 #include <mbgl/util/run_loop.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/util/io.hpp>
 
 #include <memory>
@@ -273,9 +272,8 @@ TEST(Layer, DuplicateLayer) {
     util::RunLoop loop;
 
     // Setup style
-    ThreadPool threadPool{ 1 };
     StubFileSource fileSource;
-    Style::Impl style { threadPool, fileSource, 1.0 };
+    Style::Impl style { fileSource, 1.0 };
     style.loadJSON(util::read_file("test/fixtures/resources/style-unused-sources.json"));
 
     // Add initial layer