Trace base class Event in SpeechRecognitionError.

R=sigbjornf@opera.com
BUG=

Review URL: https://codereview.chromium.org/183683007

git-svn-id: svn://svn.chromium.org/blink/trunk@168133 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/speech/SpeechRecognitionError.h

@@ -64,7 +64,10 @@ public:
 
     virtual const AtomicString& interfaceName() const OVERRIDE;
 
-    virtual void trace(Visitor*) OVERRIDE { }
+    virtual void trace(Visitor* visitor) OVERRIDE
+    {
+        Event::trace(visitor);
+    }
 
 private:
     SpeechRecognitionError(const String&, const String&);