[core] Custom layers

src/mbgl/map/map_context.cpp

@@ -11,6 +11,7 @@
 #include <mbgl/storage/response.hpp>
 
 #include <mbgl/style/style.hpp>
+#include <mbgl/style/style_layer.hpp>
 
 #include <mbgl/sprite/sprite_atlas.hpp>
 #include <mbgl/sprite/sprite_store.hpp>
@@ -277,6 +278,10 @@ double MapContext::getTopOffsetPixelsForAnnotationIcon(const std::string& name)
     return data.getAnnotationManager()->getTopOffsetPixelsForIcon(name);
 }
 
+void MapContext::addLayer(std::unique_ptr<StyleLayer> layer, mapbox::util::optional<std::string> after) {
+    style->addLayer(std::move(layer), after);
+}
+
 void MapContext::setSourceTileCacheSize(size_t size) {
     assert(util::ThreadContext::currentlyOn(util::ThreadType::Map));
     if (size != sourceCacheSize) {