Makes RenderFrameObserver/RenderViewObserver::OnDestruct pure virtual.

content/renderer/text_input_client_observer.cc

Index: content/renderer/text_input_client_observer.cc
diff --git a/content/renderer/text_input_client_observer.cc b/content/renderer/text_input_client_observer.cc
index e3b8bd7a377916830085025ed3eca9f3f8856c49..3c953eebaad238155ab72433c28dbed90b5422e2 100644
--- a/content/renderer/text_input_client_observer.cc
+++ b/content/renderer/text_input_client_observer.cc
@@ -48,6 +48,10 @@ bool TextInputClientObserver::OnMessageReceived(const IPC::Message& message) {
   return handled;
 }
 
+void TextInputClientObserver::OnDestruct() {
+  delete this;
+}
+
 blink::WebView* TextInputClientObserver::webview() {
   return render_view()->GetWebView();
 }