Introduce RenderProcessHostObserver, use it in its first client.

content/public/browser/render_process_host.h

Index: content/public/browser/render_process_host.h
diff --git a/content/public/browser/render_process_host.h b/content/public/browser/render_process_host.h
index 3aedc59ed4b8dc722dfb483e70cc3d722e03688c..765582548711909e76d308fba161a51804583d70 100644
--- a/content/public/browser/render_process_host.h
+++ b/content/public/browser/render_process_host.h
@@ -26,6 +26,7 @@ class TimeDelta;
 namespace content {
 class BrowserContext;
 class BrowserMessageFilter;
+class RenderProcessHostObserver;
 class RenderWidgetHost;
 class StoragePartition;
 
@@ -55,6 +56,8 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
     int exit_code;
   };
 
+  // General functions ---------------------------------------------------------
+
   virtual ~RenderProcessHost() {}
 
   // Initialize the new renderer process, returning true on success. This must
@@ -73,6 +76,12 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
   virtual void AddRoute(int32 routing_id, IPC::Listener* listener) = 0;
   virtual void RemoveRoute(int32 routing_id) = 0;
 
+  // Add and remove observers for lifecycle events. The order in which
+  // notifications are sent to observers is undefined. Observers must be sure to
+  // remove the observer before they go away.
+  virtual void AddObserver(RenderProcessHostObserver* observer) = 0;
+  virtual void RemoveObserver(RenderProcessHostObserver* observer) = 0;
+
   // Called to wait for the next UpdateRect message for the specified render
   // widget.  Returns true if successful, and the msg out-param will contain a
   // copy of the received UpdateRect message.