Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

android_webview/renderer/aw_render_frame_ext.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 "android_webview/common/aw_hit_test_data.h"
 #include "android_webview/common/render_view_messages.h"
 #include "android_webview/renderer/aw_render_frame_ext.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/public/renderer/android_content_detection_prefixes.h"
 #include "content/public/renderer/document_state.h"
@@ skipping 284 matching lines @@
   return render_frame()->GetRenderView()->GetWebView();
 }
 
 blink::WebFrameWidget* AwRenderFrameExt::GetWebFrameWidget() {
   if (!render_frame() || !render_frame()->GetRenderView())
     return nullptr;
 
   return render_frame()->GetRenderView()->GetWebFrameWidget();
 }
 
+void AwRenderFrameExt::OnDestruct() {
+  delete this;
+}
+
 }  // namespace android_webview