Standardize usage of virtual/override/final in components/

BUG=417463
[email protected]

Review URL: https://codereview.chromium.org/666133002

Cr-Commit-Position: refs/heads/master@{#300456}
diff --git a/components/domain_reliability/util.h b/components/domain_reliability/util.h
index 6b142c66..80699d43 100644
--- a/components/domain_reliability/util.h
+++ b/components/domain_reliability/util.h
@@ -74,12 +74,12 @@
  public:
   ActualTime();
 
-  virtual ~ActualTime();
+  ~ActualTime() override;
 
   // MockableTime implementation:
-  virtual base::Time Now() override;
-  virtual base::TimeTicks NowTicks() override;
-  virtual scoped_ptr<MockableTime::Timer> CreateTimer() override;
+  base::Time Now() override;
+  base::TimeTicks NowTicks() override;
+  scoped_ptr<MockableTime::Timer> CreateTimer() override;
 };
 
 }  // namespace domain_reliability