[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, 4 deletions

diff --git a/test/text/local_glyph_rasterizer.test.cpp b/test/text/local_glyph_rasterizer.test.cpp
index 20f825c935..5c03945b8c 100644
--- a/test/text/local_glyph_rasterizer.test.cpp
+++ b/test/text/local_glyph_rasterizer.test.cpp
@@ -7,7 +7,6 @@
 #include <mbgl/util/color.hpp>
 #include <mbgl/renderer/renderer.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/style/style.hpp>
 
 /*
@@ -33,17 +32,16 @@ namespace {
 class LocalGlyphRasterizerTest {
 public:
     LocalGlyphRasterizerTest(const optional<std::string> fontFamily)
-        : frontend(pixelRatio, fileSource, threadPool, optional<std::string>(), GLContextMode::Unique, fontFamily)
+        : frontend(pixelRatio, fileSource, optional<std::string>(), GLContextMode::Unique, fontFamily)
     {
     }
 
     util::RunLoop loop;
     StubFileSource fileSource;
-    ThreadPool threadPool { 4 };
     float pixelRatio { 1 };
     HeadlessFrontend frontend;
     Map map { frontend, MapObserver::nullObserver(), frontend.getSize(), pixelRatio, fileSource,
-              threadPool, MapOptions().withMapMode(MapMode::Static)};
+              MapOptions().withMapMode(MapMode::Static)};
 
     void checkRendering(const char * name) {
         test::checkImage(std::string("test/fixtures/local_glyphs/") + name,