[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, 5 insertions, 0 deletions

diff --git a/include/mbgl/actor/scheduler.hpp b/include/mbgl/actor/scheduler.hpp
index 75ead29f0a..6470ab1245 100644
--- a/include/mbgl/actor/scheduler.hpp
+++ b/include/mbgl/actor/scheduler.hpp
@@ -41,6 +41,11 @@ public:
     // Set/Get the current Scheduler for this thread
     static Scheduler* GetCurrent();
     static void SetCurrent(Scheduler*);
+
+    // Get the scheduler for asynchronous tasks. This method
+    // will lazily initialize a shared worker pool when ran
+    // from the first time.
+    static std::shared_ptr<Scheduler> GetBackground();
 };
 
 } // namespace mbgl