Introduce RenderProcessHostObserver, use it in its first client.

content/public/browser/render_process_host_observer.h

Index: content/public/browser/render_process_host_observer.h
diff --git a/content/public/browser/render_process_host_observer.h b/content/public/browser/render_process_host_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..221673734fbc62aea6a1eeb798793daf75814784
--- /dev/null
+++ b/content/public/browser/render_process_host_observer.h
@@ -0,0 +1,27 @@
+// Copyright 2013 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.
+
+#ifndef CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_
+#define CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_
+
+#include "content/common/content_export.h"
+
+namespace content {
+
+class RenderProcessHost;
+
+// An observer API implemented by classes which are interested
+// in RenderProcessHost lifecycle events.
+class CONTENT_EXPORT RenderProcessHostObserver {
+ public:
+  // Called when the observed RenderProcessHost itself is destroyed.
+  virtual void RenderProcessHostDestroyed(RenderProcessHost* host) {}
+
+ protected:
+  virtual ~RenderProcessHostObserver() {}
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_OBSERVER_H_