Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/content_settings_observer.cc

Index: chrome/renderer/content_settings_observer.cc
diff --git a/chrome/renderer/content_settings_observer.cc b/chrome/renderer/content_settings_observer.cc
index 661c941e7ef71b0cf18d67ee24167156855bfd35..8bf046741d65ffa0b06a4183bd22d5d53de35c2c 100644
--- a/chrome/renderer/content_settings_observer.cc
+++ b/chrome/renderer/content_settings_observer.cc
@@ -248,6 +248,10 @@ void ContentSettingsObserver::DidCommitProvisionalLoad(
          !url.SchemeIs(url::kDataScheme));
 }
 
+void ContentSettingsObserver::OnDestruct() {
+  delete this;
+}
+
 bool ContentSettingsObserver::allowDatabase(const WebString& name,
                                             const WebString& display_name,
                                             unsigned long estimated_size) {