webserver: Fix potential memory leak in libwebserv

libwebserv::RequestHandlerInterface was missing a virtual destructor
and could potentially leak memory for members of classes deriving
from this interface

BUG=None
TEST=`FEATURES=test emerge-link webserver`

Change-Id: I3be46c4305a5b357ab854cf1d4bf2cec3bf7fea9
Reviewed-on: https://chromium-review.googlesource.com/272959
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
diff --git a/libwebserv/request_handler_interface.h b/libwebserv/request_handler_interface.h
index 878c975..a373680 100644
--- a/libwebserv/request_handler_interface.h
+++ b/libwebserv/request_handler_interface.h
@@ -20,6 +20,7 @@
  public:
   using HandlerSignature =
       void(std::unique_ptr<Request>, std::unique_ptr<Response>);
+  virtual ~RequestHandlerInterface() = default;
 
   virtual void HandleRequest(std::unique_ptr<Request> request,
                              std::unique_ptr<Response> response) = 0;