Standardize usage of virtual/override/final specifiers in base/.

base/memory/discardable_memory_manager_unittest.cc

Index: base/memory/discardable_memory_manager_unittest.cc
diff --git a/base/memory/discardable_memory_manager_unittest.cc b/base/memory/discardable_memory_manager_unittest.cc
index 12f7f0816a50f2097272075f25ace4a19feef601..9f06e3738c3f6b1ad7c53b8c81311e5e525d2788 100644
--- a/base/memory/discardable_memory_manager_unittest.cc
+++ b/base/memory/discardable_memory_manager_unittest.cc
@@ -33,7 +33,7 @@ class TestAllocationImpl : public internal::DiscardableMemoryManagerAllocation {
     DCHECK(is_allocated_);
     is_allocated_ = false;
   }
-  virtual bool IsMemoryResident() const override {
+  bool IsMemoryResident() const override {
     DCHECK(is_allocated_);
     return true;
   }
@@ -460,9 +460,9 @@ class ThreadedDiscardableMemoryManagerTest
       : memory_usage_thread_("memory_usage_thread"),
         thread_sync_(true, false) {}
 
-  virtual void SetUp() override { memory_usage_thread_.Start(); }
+  void SetUp() override { memory_usage_thread_.Start(); }
 
-  virtual void TearDown() override { memory_usage_thread_.Stop(); }
+  void TearDown() override { memory_usage_thread_.Stop(); }
 
   void UseMemoryHelper() {
     size_t size = 1024;