update_engine: fix -Winconsistent-missing-override warning

BUG=chromium:453566
TEST=FEATURES="test" emerge-amd64-generic update_engine

Change-Id: Icf889d01021993e6b3175b3a15efe82069d2d2fc
Reviewed-on: https://chromium-review.googlesource.com/244411
Reviewed-by: Alex Deymo <deymo@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
diff --git a/download_action_unittest.cc b/download_action_unittest.cc
index 5825286..0bb0732 100644
--- a/download_action_unittest.cc
+++ b/download_action_unittest.cc
@@ -59,8 +59,8 @@
   ~DownloadActionTestProcessorDelegate() override {
     EXPECT_TRUE(processing_done_called_);
   }
-  virtual void ProcessingDone(const ActionProcessor* processor,
-                              ErrorCode code) {
+  void ProcessingDone(const ActionProcessor* processor,
+                      ErrorCode code) override {
     ASSERT_TRUE(loop_);
     g_main_loop_quit(loop_);
     vector<char> found_data;
@@ -74,9 +74,9 @@
     processing_done_called_ = true;
   }
 
-  virtual void ActionCompleted(ActionProcessor* processor,
-                               AbstractAction* action,
-                               ErrorCode code) {
+  void ActionCompleted(ActionProcessor* processor,
+                       AbstractAction* action,
+                       ErrorCode code) override {
     const string type = action->Type();
     if (type == DownloadAction::StaticType()) {
       EXPECT_EQ(expected_code_, code);