Merge branch 'master' of https://github.com/mapbox/mapbox-gl-native into android-mason

Conflicts:
	gyp/common.gypi
	include/mbgl/geometry/vao.hpp
	include/mbgl/platform/event.hpp
	include/mbgl/platform/gl.hpp
	platform/default/http_request_baton_curl.cpp
	src/storage/response.cpp

src/map/tile_data.cpp

@@ -75,7 +75,10 @@ void TileData::request() {
 void TileData::cancel() {
     if (state != State::obsolete) {
         state = State::obsolete;
-        req.reset();
+        if (req) {
+            req->cancel();
+            req.reset();
+        }
     }
 }