Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/public/renderer/render_view_observer.cc

Index: content/public/renderer/render_view_observer.cc
diff --git a/content/public/renderer/render_view_observer.cc b/content/public/renderer/render_view_observer.cc
index 5e876cc1bff979fbb4fd2e8e70a5d00e81b00b02..f90a8058cb44d8cc2a73b0169b7ec5b2f6fe9373 100644
--- a/content/public/renderer/render_view_observer.cc
+++ b/content/public/renderer/render_view_observer.cc
@@ -24,10 +24,6 @@ RenderViewObserver::~RenderViewObserver() {
     render_view_->RemoveObserver(this);
 }
 
-void RenderViewObserver::OnDestruct() {
-  delete this;
-}
-
 bool RenderViewObserver::OnMessageReceived(const IPC::Message& message) {
   return false;
 }