Standardize usage of virtual/override/final in cc/

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index 5fc01fc9d2dbeeef00999624053ac90a670c7f34..206ec60776699eaec2688670de3c7543318614d6 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -49,17 +49,16 @@ class LayerScrollOffsetDelegateProxy : public LayerImpl::ScrollOffsetDelegate {
   }
 
   // LayerScrollOffsetDelegate implementation.
-  virtual void SetTotalScrollOffset(
-      const gfx::ScrollOffset& new_offset) override {
+  void SetTotalScrollOffset(const gfx::ScrollOffset& new_offset) override {
     last_set_scroll_offset_ = new_offset;
     layer_tree_impl_->UpdateScrollOffsetDelegate();
   }
 
-  virtual gfx::ScrollOffset GetTotalScrollOffset() override {
+  gfx::ScrollOffset GetTotalScrollOffset() override {
     return layer_tree_impl_->GetDelegatedScrollOffset(layer_);
   }
 
-  virtual bool IsExternalFlingActive() const override {
+  bool IsExternalFlingActive() const override {
     return delegate_->IsExternalFlingActive();
   }