GstChromiumHttpSrc: define GUniquePtr<GstStructure> as done in WTF
GstChromiumHttpSrc: define GUniquePtr<GstStructure> as done in WTF

We should move these definitions to a separate header if we need it
for more types and other places.

Found while running in debug mode.

lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend