move worker to MapContext

src/mbgl/map/map_context.cpp

@@ -11,6 +11,7 @@
 
 #include <mbgl/util/std.hpp>
 #include <mbgl/util/uv_detail.hpp>
+#include <mbgl/util/worker.hpp>
 #include <mbgl/util/texture_pool.hpp>
 
 namespace mbgl {
@@ -24,4 +25,9 @@ MapContext::MapContext(Environment& env)
       painter(util::make_unique<Painter>(*spriteAtlas, *glyphAtlas, *lineAtlas)) {
 }
 
+Worker& MapContext::getWorker() {
+    assert(workers);
+    return *workers;
+}
+
 }