address comments

include/mbgl/gfx/context.hpp

@@ -52,7 +52,9 @@ using UniqueDrawableBuilder = std::unique_ptr<DrawableBuilder>;
 using VertexAttributeArrayPtr = std::shared_ptr<VertexAttributeArray>;
 #endif
 
-static ContextObserver nullObserver;
+namespace {
+    ContextObserver nullObserver;
+}
 
 class Context {
 protected:

include/mbgl/tile/tile_operation.hpp

@@ -3,14 +3,14 @@
 
 namespace mbgl {
 enum class TileOperation : uint8_t {
-    RequestedFromCache,
-    RequestedFromNetwork,
-    LoadFromNetwork,
-    LoadFromCache,
-    StartParse,
-    EndParse,
-    Error,
-    Cancelled,
-    NullOp,
+    RequestedFromCache, ///< A read request from the cache
+    RequestedFromNetwork, ///< A read request from the online source
+    LoadFromNetwork, ///< Tile data from the network has been retrieved
+    LoadFromCache, ///< Tile data from the cache has been retrieved
+    StartParse, ///< Background processing of tile data has been initiated
+    EndParse, ///< Background processing of tile data has been completed
+    Error, ///< An error occurred while loading the tile
+    Cancelled, ///< Loading of a tile was cancelled
+    NullOp, ///< No operation has taken place
 };
 } // namespace mbgl

test/map/map.test.cpp

@@ -1695,10 +1695,6 @@ TEST(Map, ObserveTileLifecycle) {
         OverscaledTileID id;
         std::string sourceID;
         TileOperation op;
-
-        bool operator==(const TileEntry& other) const noexcept {
-            return id == other.id && sourceID == other.sourceID && op == other.op;
-        }
     };
     std::mutex tileMutex;
     std::vector<TileEntry> tileOps;