Convert Style to unique_ptr and pass by reference

Fixes #1277
Fixes #1309

src/mbgl/map/live_tile_data.cpp

@@ -11,7 +11,7 @@ using namespace mbgl;
 LiveTileData::LiveTileData(const TileID& id_,
                            AnnotationManager& annotationManager_,
                            float mapMaxZoom,
-                           util::ptr<Style> style_,
+                           Style& style_,
                            GlyphAtlas& glyphAtlas_,
                            GlyphStore& glyphStore_,
                            SpriteAtlas& spriteAtlas_,
@@ -35,27 +35,16 @@ void LiveTileData::parse() {
 
     if (tile) {
         try {
-            if (!style) {
-                throw std::runtime_error("style isn't present in LiveTileData object anymore");
-            }
-
             // Parsing creates state that is encapsulated in TileParser. While parsing,
             // the TileParser object writes results into this objects. All other state
             // is going to be discarded afterwards.
             TileParser parser(*tile, *this, style, glyphAtlas, glyphStore, spriteAtlas, sprite);
-
-            // Clear the style so that we don't have a cycle in the shared_ptr references.
-            style.reset();
-
             parser.parse();
         } catch (const std::exception& ex) {
             Log::Error(Event::ParseTile, "Live-parsing [%d/%d/%d] failed: %s", id.z, id.x, id.y, ex.what());
             state = State::obsolete;
             return;
         }
-    } else {
-        // Clear the style so that we don't have a cycle in the shared_ptr references.
-        style.reset();
     }
 
     if (state != State::obsolete) {