Standardize usage of virtual/override/final in content/browser/

This patch was automatically generated by applying clang fixit hints
generated by the plugin to the source tree.

BUG=417463
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Review URL: https://codereview.chromium.org/667943003

Cr-Commit-Position: refs/heads/master@{#300469}
diff --git a/content/browser/browser_process_sub_thread.h b/content/browser/browser_process_sub_thread.h
index 888db2d0..5899fa3 100644
--- a/content/browser/browser_process_sub_thread.h
+++ b/content/browser/browser_process_sub_thread.h
@@ -35,11 +35,11 @@
 class CONTENT_EXPORT BrowserProcessSubThread : public BrowserThreadImpl {
  public:
   explicit BrowserProcessSubThread(BrowserThread::ID identifier);
-  virtual ~BrowserProcessSubThread();
+  ~BrowserProcessSubThread() override;
 
  protected:
-  virtual void Init() override;
-  virtual void CleanUp() override;
+  void Init() override;
+  void CleanUp() override;
 
  private:
   // These methods encapsulate cleanup that needs to happen on the IO thread