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/rappor/byte_vector_utils.h b/components/rappor/byte_vector_utils.h
index a3f5f06e..3090d9b 100644
--- a/components/rappor/byte_vector_utils.h
+++ b/components/rappor/byte_vector_utils.h
@@ -80,7 +80,7 @@
                           const std::string& entropy_input,
                           const std::string& personalization_string);
 
-  virtual ~HmacByteVectorGenerator();
+  ~HmacByteVectorGenerator() override;
 
   // Generates a random string suitable for passing to the constructor as
   // |entropy_input|.
@@ -95,7 +95,7 @@
   explicit HmacByteVectorGenerator(const HmacByteVectorGenerator& prev_request);
 
   // ByteVector implementation:
-  virtual ByteVector GetRandomByteVector() override;
+  ByteVector GetRandomByteVector() override;
 
  private:
   // HMAC initalized with the value of "Key" HMAC_DRBG_Initialize.