Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/banners/app_banner_client.cc

Index: chrome/renderer/banners/app_banner_client.cc
diff --git a/chrome/renderer/banners/app_banner_client.cc b/chrome/renderer/banners/app_banner_client.cc
index 215fa29026b0b26c401c519a7daea831ca3b8e72..deec5d66bf8512e34b00bd3f420fee4f0825458d 100644
--- a/chrome/renderer/banners/app_banner_client.cc
+++ b/chrome/renderer/banners/app_banner_client.cc
@@ -17,12 +17,7 @@ AppBannerClient::AppBannerClient(content::RenderFrame* render_frame)
 AppBannerClient::~AppBannerClient() {
 }
 
-void AppBannerClient::OnDestruct() {
-  // The RenderFrameImpl destructor calls RenderFrameObserver::OnDestruct, which
-  // deletes this object. However, RenderFrameImpl also holds a scoped pointer
-  // to AppBannerClient. Override OnDestruct to be a no-op to stop a double call
-  // to the destructor and a renderer crash.
-}
+void AppBannerClient::OnDestruct() {}
 
 bool AppBannerClient::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;