Standardize usage of virtual/override/final specifiers.

extensions/browser/api/dns/dns_apitest.cc

Index: extensions/browser/api/dns/dns_apitest.cc
diff --git a/extensions/browser/api/dns/dns_apitest.cc b/extensions/browser/api/dns/dns_apitest.cc
index 5d620177e17ca3bc00d4ff5c9dd8ac8119768686..24586f9dafbdaa0ee5da1db117ef6b4dd43a20d4 100644
--- a/extensions/browser/api/dns/dns_apitest.cc
+++ b/extensions/browser/api/dns/dns_apitest.cc
@@ -26,13 +26,13 @@ class DnsApiTest : public ShellApiTest {
   DnsApiTest() : resolver_creator_(new MockHostResolverCreator()) {}
 
  private:
-  virtual void SetUpOnMainThread() override {
+  void SetUpOnMainThread() override {
     ShellApiTest::SetUpOnMainThread();
     HostResolverWrapper::GetInstance()->SetHostResolverForTesting(
         resolver_creator_->CreateMockHostResolver());
   }
 
-  virtual void TearDownOnMainThread() override {
+  void TearDownOnMainThread() override {
     HostResolverWrapper::GetInstance()->SetHostResolverForTesting(NULL);
     resolver_creator_->DeleteMockHostResolver();
     ShellApiTest::TearDownOnMainThread();