[node, tests] Consolidate headless rendering logic in HeadlessFrontend

platform/node/src/node_map.hpp

@@ -4,8 +4,7 @@
 
 #include <mbgl/map/map.hpp>
 #include <mbgl/storage/file_source.hpp>
-#include <mbgl/gl/headless_backend.hpp>
-#include <mbgl/gl/offscreen_view.hpp>
+#include <mbgl/util/image.hpp>
 
 #include <exception>
 
@@ -15,15 +14,13 @@
 #include <nan.h>
 #pragma GCC diagnostic pop
 
-namespace node_mbgl {
-    
-class NodeRendererFrontend;
+namespace mbgl {
+class Map;
+class HeadlessFrontend;
+} // namespace mbgl
+
+namespace node_mbgl {
 
-class NodeBackend : public mbgl::HeadlessBackend {
-public:
-    NodeBackend();
-};
-    
 class NodeMapObserver : public mbgl::MapObserver {
     void onDidFailLoadingMap(std::exception_ptr) override;
 };
@@ -73,11 +70,9 @@ public:
     std::unique_ptr<mbgl::AsyncRequest> request(const mbgl::Resource&, mbgl::FileSource::Callback);
 
     const float pixelRatio;
-    NodeBackend backend;
-    std::unique_ptr<mbgl::OffscreenView> view;
     NodeThreadPool threadpool;
     NodeMapObserver mapObserver;
-    std::unique_ptr<NodeRendererFrontend> rendererFrontend;
+    std::unique_ptr<mbgl::HeadlessFrontend> frontend;
     std::unique_ptr<mbgl::Map> map;
 
     std::exception_ptr error;