[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`.

2 files changed, 5 insertions, 6 deletions

diff --git a/src/mbgl/sprite/sprite_loader.cpp b/src/mbgl/sprite/sprite_loader.cpp
index ce8fbe5894..bfb0c570d6 100644
--- a/src/mbgl/sprite/sprite_loader.cpp
+++ b/src/mbgl/sprite/sprite_loader.cpp
@@ -20,9 +20,9 @@ namespace mbgl {
 static SpriteLoaderObserver nullObserver;
 
 struct SpriteLoader::Loader {
-    Loader(Scheduler& scheduler, SpriteLoader& imageManager)
+    Loader(SpriteLoader& imageManager)
         : mailbox(std::make_shared<Mailbox>(*Scheduler::GetCurrent())),
-          worker(scheduler, ActorRef<SpriteLoader>(imageManager, mailbox)) {
+          worker(Scheduler::GetBackground(), ActorRef<SpriteLoader>(imageManager, mailbox)) {
     }
 
     std::shared_ptr<const std::string> image;
@@ -40,14 +40,14 @@ SpriteLoader::SpriteLoader(float pixelRatio_)
 
 SpriteLoader::~SpriteLoader() = default;
 
-void SpriteLoader::load(const std::string& url, Scheduler& scheduler, FileSource& fileSource) {
+void SpriteLoader::load(const std::string& url, FileSource& fileSource) {
     if (url.empty()) {
         // Treat a non-existent sprite as a successfully loaded empty sprite.
         observer->onSpriteLoaded({});
         return;
     }
 
-    loader = std::make_unique<Loader>(scheduler, *this);
+    loader = std::make_unique<Loader>(*this);
 
     loader->jsonRequest = fileSource.request(Resource::spriteJSON(url, pixelRatio), [this](Response res) {
         if (res.error) {
diff --git a/src/mbgl/sprite/sprite_loader.hpp b/src/mbgl/sprite/sprite_loader.hpp
index 0daf46be9c..0b7d37fa14 100644
--- a/src/mbgl/sprite/sprite_loader.hpp
+++ b/src/mbgl/sprite/sprite_loader.hpp
@@ -12,7 +12,6 @@
 
 namespace mbgl {
 
-class Scheduler;
 class FileSource;
 class SpriteLoaderObserver;
 
@@ -21,7 +20,7 @@ public:
     SpriteLoader(float pixelRatio);
     ~SpriteLoader();
 
-    void load(const std::string& url, Scheduler&, FileSource&);
+    void load(const std::string& url, FileSource&);
 
     void setObserver(SpriteLoaderObserver*);