update_engine: Enforce virtual destructors on virtual classes.

This patch enables -Wnon-virtual-dtor enforcing that virtual classes
such as interfaces have a virtual destructor. This is required by
the Google Coding Style and avoids some problems where the derived
class' destructor is not called.

BUG=None
TEST=FEATURES=test emerge-link update_engine

Change-Id: Id907e3c14923fcccc20b83bd064fa9c9c51fffb3
Reviewed-on: https://chromium-review.googlesource.com/228927
Commit-Queue: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/omaha_request_params.h b/omaha_request_params.h
index 94db475..0657649 100644
--- a/omaha_request_params.h
+++ b/omaha_request_params.h
@@ -91,6 +91,8 @@
         force_lock_down_(false),
         forced_lock_down_(false) {}
 
+  virtual ~OmahaRequestParams() = default;
+
   // Setters and getters for the various properties.
   inline std::string os_platform() const { return os_platform_; }
   inline std::string os_version() const { return os_version_; }