Fix resource leaks in drm hal

bug:36408047
test: manual tests to verify leaks are fixed
Change-Id: Idd79e99e211d81f8b3e58cf52c9b01ce9d370dc4
diff --git a/drm/1.0/default/CryptoPlugin.h b/drm/1.0/default/CryptoPlugin.h
index 11cc2aa..5da469c 100644
--- a/drm/1.0/default/CryptoPlugin.h
+++ b/drm/1.0/default/CryptoPlugin.h
@@ -44,7 +44,7 @@
 struct CryptoPlugin : public ICryptoPlugin {
     CryptoPlugin(android::CryptoPlugin *plugin) : mLegacyPlugin(plugin) {}
 
-    ~CryptoPlugin() {delete mLegacyPlugin;}
+    virtual ~CryptoPlugin() {delete mLegacyPlugin;}
 
     // Methods from ::android::hardware::drm::V1_0::ICryptoPlugin
     // follow.