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

cc/input/scroll_elasticity_helper.cc

Index: cc/input/scroll_elasticity_helper.cc
diff --git a/cc/input/scroll_elasticity_helper.cc b/cc/input/scroll_elasticity_helper.cc
index 7065e86a4911e236cecbf1912d9e87bd53cbc037..e5bbe2beba1ed34fd6985ad648feec61d6eacf6c 100644
--- a/cc/input/scroll_elasticity_helper.cc
+++ b/cc/input/scroll_elasticity_helper.cc
@@ -13,7 +13,7 @@ namespace cc {
 class ScrollElasticityHelperImpl : public ScrollElasticityHelper {
  public:
   explicit ScrollElasticityHelperImpl(LayerTreeHostImpl* layer_tree_host_impl);
-  virtual ~ScrollElasticityHelperImpl();
+  ~ScrollElasticityHelperImpl() override;
 
   // The amount that the view is stretched past the normal allowable bounds.
   // The "overhang" amount.