[core] Source::setVolatile enables Resource::StoragePolicy::Volatile for tiles

src/mbgl/renderer/tile_pyramid.cpp

@@ -93,6 +93,7 @@ void TilePyramid::update(const std::vector<Immutable<style::LayerProperties>>& l
     const optional<uint8_t>& sourcePrefetchZoomDelta = sourceImpl.getPrefetchZoomDelta();
     const optional<uint8_t>& maxParentTileOverscaleFactor = sourceImpl.getMaxOverscaleFactorForParentTiles();
     const Duration minimumUpdateInterval = sourceImpl.getMinimumTileUpdateInterval();
+    const bool isVolatile = sourceImpl.isVolatile();
 
     std::vector<OverscaledTileID> idealTiles;
     std::vector<OverscaledTileID> panTiles;
@@ -132,7 +133,7 @@ void TilePyramid::update(const std::vector<Immutable<style::LayerProperties>>& l
 
     auto retainTileFn = [&](Tile& tile, TileNecessity necessity) -> void {
         if (retain.emplace(tile.id).second) {
-            tile.setUpdateParameters({minimumUpdateInterval});
+            tile.setUpdateParameters({minimumUpdateInterval, isVolatile});
             tile.setNecessity(necessity);
         }
 

src/mbgl/tile/tile.hpp

@@ -36,10 +36,11 @@ class UploadPass;
 
 struct TileUpdateParameters {
     Duration minimumUpdateInterval;
+    bool isVolatile;
 };
 
 inline bool operator==(const TileUpdateParameters& a, const TileUpdateParameters& b) {
-    return a.minimumUpdateInterval == b.minimumUpdateInterval;
+    return a.minimumUpdateInterval == b.minimumUpdateInterval && a.isVolatile == b.isVolatile;
 }
 
 inline bool operator!=(const TileUpdateParameters& a, const TileUpdateParameters& b) {

src/mbgl/tile/tile_loader.hpp

@@ -49,7 +49,7 @@ private:
     Resource resource;
     std::shared_ptr<FileSource> fileSource;
     std::unique_ptr<AsyncRequest> request;
-    TileUpdateParameters updateParameters{{Duration::zero()}};
+    TileUpdateParameters updateParameters{Duration::zero(), false};
 };
 
 } // namespace mbgl

src/mbgl/tile/tile_loader_impl.hpp

@@ -160,6 +160,8 @@ void TileLoader<T>::loadFromNetwork() {
     // NetworkOnly request.
     resource.loadingMethod = Resource::LoadingMethod::NetworkOnly;
     resource.minimumUpdateInterval = updateParameters.minimumUpdateInterval;
+    resource.storagePolicy =
+        updateParameters.isVolatile ? Resource::StoragePolicy::Volatile : Resource::StoragePolicy::Permanent;
     request = fileSource->request(resource, [this](const Response& res) { loadedData(res); });
 }