update_engine: Add override when possible.

Google Style Guide requires to include the "override" keyword
when overriding a method on a derived class, so the compiler will
catch errors if the method is not overriding a member of the base
class.

This patch introduces the "override" keyword when possible.

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

Change-Id: Ie83d115c5730f3b35b3d95859a54bc1a48e0be7b
Reviewed-on: https://chromium-review.googlesource.com/228928
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
diff --git a/omaha_request_action_unittest.cc b/omaha_request_action_unittest.cc
index 227dde7..f358c39 100644
--- a/omaha_request_action_unittest.cc
+++ b/omaha_request_action_unittest.cc
@@ -50,7 +50,7 @@
 
 class OmahaRequestActionTest : public ::testing::Test {
  protected:
-  void SetUp() {
+  void SetUp() override {
     fake_system_state_.set_request_params(&request_params_);
     fake_system_state_.set_prefs(&fake_prefs_);
   }
@@ -223,7 +223,7 @@
   OmahaRequestActionTestProcessorDelegate()
       : loop_(nullptr),
         expected_code_(ErrorCode::kSuccess) {}
-  virtual ~OmahaRequestActionTestProcessorDelegate() {
+  ~OmahaRequestActionTestProcessorDelegate() override {
   }
   virtual void ProcessingDone(const ActionProcessor* processor,
                               ErrorCode code) {