Implement lifetime observer on RenderWidgetHostViewBase.

content/browser/renderer_host/render_widget_host_view_base_observer.cc

Index: content/browser/renderer_host/render_widget_host_view_base_observer.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_base_observer.cc b/content/browser/renderer_host/render_widget_host_view_base_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..92f1247d12fe6e472592e4f771bb10fbb3e3d8aa
--- /dev/null
+++ b/content/browser/renderer_host/render_widget_host_view_base_observer.cc
@@ -0,0 +1,14 @@
+// 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 "content/browser/renderer_host/render_widget_host_view_base_observer.h"
+
+namespace content {
+
+RenderWidgetHostViewBaseObserver::~RenderWidgetHostViewBaseObserver() {}
+
+void RenderWidgetHostViewBaseObserver::OnRenderWidgetHostViewBaseDestroyed(
+    RenderWidgetHostViewBase*) {}
+
+}  // namespace content