Move the Collision object from TileParser to VectorTileData

We keep the Collision object alive longer because we need it
for the SymbolBuckets yet to be created in case more data
resources arrive. When the tile is no longer needed or if it
is completely parsed or obsolete (i.e. in a immutable state)
we throw the Collision object away.

src/mbgl/map/vector_tile_data.cpp

@@ -6,6 +6,7 @@
 #include <mbgl/map/source.hpp>
 #include <mbgl/geometry/glyph_atlas.hpp>
 #include <mbgl/platform/log.hpp>
+#include <mbgl/text/collision.hpp>
 #include <mbgl/util/pbf.hpp>
 
 using namespace mbgl;
@@ -19,12 +20,13 @@ VectorTileData::VectorTileData(const TileID& id_,
                                util::ptr<Sprite> sprite_,
                                const SourceInfo& source_)
     : TileData(id_, source_),
+      depth(id_.z >= source_.max_zoom ? mapMaxZoom - id_.z : 1),
       glyphAtlas(glyphAtlas_),
       glyphStore(glyphStore_),
       spriteAtlas(spriteAtlas_),
       sprite(sprite_),
       style(style_),
-      depth(id.z >= source.max_zoom ? mapMaxZoom - id.z : 1) {
+      collision(util::make_unique<Collision>(id_.z, 4096, source_.tile_size, depth)) {
 }
 
 VectorTileData::~VectorTileData() {
@@ -91,3 +93,11 @@ void VectorTileData::setBucket(StyleLayer const& layer, std::unique_ptr<Bucket>
 
     buckets[layer.bucket->name] = std::move(bucket);
 }
+
+void VectorTileData::setState(const State& state_) {
+    TileData::setState(state_);
+
+    if (isImmutable()) {
+        collision.reset();
+    }
+}