Reland: [Parse] ParseInfo owns the parsing Zone.

src/background-parsing-task.h

Index: src/background-parsing-task.h
diff --git a/src/background-parsing-task.h b/src/background-parsing-task.h
index d7fe6ba8db978b842e384c6ca762119f0c26f3fc..061e36595d1d388857059871a1425a9c4712b01a 100644
--- a/src/background-parsing-task.h
+++ b/src/background-parsing-task.h
@@ -38,7 +38,6 @@ struct StreamedSource {
   // between parsing and compilation. These need to be initialized before the
   // compilation starts.
   UnicodeCache unicode_cache;
-  std::unique_ptr<Zone> zone;
   std::unique_ptr<ParseInfo> info;
   std::unique_ptr<Parser> parser;