Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/render_frame_impl_browsertest.cc

 // Copyright 2015 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 <stdint.h>
 
 #include "base/command_line.h"
 #include "base/debug/leak_annotations.h"
 #include "build/build_config.h"
 #include "content/common/frame_messages.h"
@@ skipping 90 matching lines @@
   FakeCompositorDependencies compositor_deps_;
 };
 
 class RenderFrameTestObserver : public RenderFrameObserver {
  public:
   explicit RenderFrameTestObserver(RenderFrame* render_frame)
       : RenderFrameObserver(render_frame), visible_(false) {}
 
   ~RenderFrameTestObserver() override {}
 
+  // RenderFrameObserver implementation.
   void WasShown() override { visible_ = true; }
   void WasHidden() override { visible_ = false; }
+  void OnDestruct() override { delete this; }
 
   bool visible() { return visible_; }
 
  private:
   bool visible_;
 };
 
 #if defined(OS_ANDROID)
 // See https://crbug.com/472717
 #define MAYBE_SubframeWidget DISABLED_SubframeWidget
@@ skipping 163 matching lines @@
     EXPECT_EQ(blink::WebEffectiveConnectionType::TypeUnknown,
               GetMainRenderFrame()->getEffectiveConnectionType());
 
     // The subframe would be deleted here after a cross-document navigation.
     // It happens to be left around in this test because this does not simulate
     // the frame detach.
   }
 }
 
 }  // namespace