Make CompositorObserver’s destructor protected-and-virtual.

content/browser/renderer_host/browser_compositor_view_mac.mm

Index: content/browser/renderer_host/browser_compositor_view_mac.mm
diff --git a/content/browser/renderer_host/browser_compositor_view_mac.mm b/content/browser/renderer_host/browser_compositor_view_mac.mm
index d76f0a192b9661d02ef2183b548b328e6fb2942d..f86aa2495aeb40a83b5d8a0e34797439e1d368e6 100644
--- a/content/browser/renderer_host/browser_compositor_view_mac.mm
+++ b/content/browser/renderer_host/browser_compositor_view_mac.mm
@@ -56,7 +56,7 @@ void ReleaseSpareCompositors() {
 // in terms of time and resources).
 class RecyclableCompositorMac : public ui::CompositorObserver {
  public:
-  virtual ~RecyclableCompositorMac();
+  ~RecyclableCompositorMac() override;
 
   // Create a compositor, or recycle a preexisting one.
   static std::unique_ptr<RecyclableCompositorMac> Create();