Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/mojo_bindings_controller.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/mojo_bindings_controller.h"
 
 #include "content/common/view_messages.h"
 #include "content/public/renderer/render_frame.h"
 #include "content/public/renderer/render_view.h"
 #include "content/renderer/mojo_context_state.h"
@@ skipping 80 matching lines @@
   // lost. If this is the result of the first load then the contextstate should
   // be empty and we don't need to destroy it.
   MojoContextState* state = GetContextState();
   if (state && !state->module_added())
     return;
 
   v8::HandleScope handle_scope(blink::mainThreadIsolate());
   DestroyContextState(render_frame()->GetWebFrame()->mainWorldScriptContext());
 }
 
+void MojoBindingsController::OnDestruct() {
+  delete this;
+}
+
 }  // namespace content