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 dfe16a343820cf8ef0997e2392be7ace627ad6fd..54408b7e75a24a02524726873bcfbe9be4fdb369 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();