crash-reporter: Use C++11 override specifier.

Also remove some unnecessary 'void' arguments.

BUG=None
TEST=`FEATURES=test emerge-$BOARD crash-reporter`

Change-Id: I0039aec93aae14cb238f284fda756b631f9c1587
Reviewed-on: https://chromium-review.googlesource.com/211959
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
diff --git a/crash_reporter/user_collector.h b/crash_reporter/user_collector.h
index 3658e51..9f1bb9c 100644
--- a/crash_reporter/user_collector.h
+++ b/crash_reporter/user_collector.h
@@ -31,7 +31,7 @@
                   IsFeedbackAllowedFunction is_metrics_allowed,
                   bool generate_diagnostics);
 
-  virtual ~UserCollector();
+  ~UserCollector() override;
 
   // Enable collection.
   bool Enable() { return SetUpInternal(true); }