Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/text_input_client_observer.h

Index: content/renderer/text_input_client_observer.h
diff --git a/content/renderer/text_input_client_observer.h b/content/renderer/text_input_client_observer.h
index c41b670ce226170bc5f9bdd1002ffffd20b238e7..2c538a61c2b9813b18ae21cbb734c1d0f96bf773 100644
--- a/content/renderer/text_input_client_observer.h
+++ b/content/renderer/text_input_client_observer.h
@@ -31,6 +31,9 @@ class TextInputClientObserver : public RenderViewObserver {
   bool OnMessageReceived(const IPC::Message& message) override;
 
  private:
+  // RenderViewObserver implementation.
+  void OnDestruct() override;
+
   // Returns the WebView of the RenderView.
   blink::WebView* webview();