Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

chrome/renderer/spellchecker/spellcheck_provider.cc

 // Copyright (c) 2012 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 "chrome/renderer/spellchecker/spellcheck_provider.h"
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/spellcheck_marker.h"
@@ skipping 331 matching lines @@
         results[i].length = last_results_[i].length;
         results[i].replacement = last_results_[i].replacement;
       }
       completion->didFinishCheckingText(results);
       return true;
     }
   }
 
   return false;
 }
+
+void SpellCheckProvider::OnDestruct() {
+  delete this;
+}