Introduce RenderProcessHostObserver, use it in its first client.

content/browser/renderer_host/render_process_host_impl.h

Index: content/browser/renderer_host/render_process_host_impl.h
diff --git a/content/browser/renderer_host/render_process_host_impl.h b/content/browser/renderer_host/render_process_host_impl.h
index 681d3295cf3bf9f828414d0d1f63df157ddb4e64..98e04b30eef3109dfec0d302ba3bd558f9bd3d84 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -10,6 +10,7 @@
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
+#include "base/observer_list.h"
 #include "base/process/process.h"
 #include "base/timer/timer.h"
 #include "content/browser/child_process_launcher.h"
@@ -82,6 +83,8 @@ class CONTENT_EXPORT RenderProcessHostImpl
   virtual int GetNextRoutingID() OVERRIDE;
   virtual void AddRoute(int32 routing_id, IPC::Listener* listener) OVERRIDE;
   virtual void RemoveRoute(int32 routing_id) OVERRIDE;
+  virtual void AddObserver(RenderProcessHostObserver* observer) OVERRIDE;
+  virtual void RemoveObserver(RenderProcessHostObserver* observer) OVERRIDE;
   virtual bool WaitForBackingStoreMsg(int render_widget_id,
                                       const base::TimeDelta& max_delay,
                                       IPC::Message* msg) OVERRIDE;
@@ -307,6 +310,9 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // Owned by |browser_context_|.
   StoragePartitionImpl* storage_partition_impl_;
 
+  // The observers watching our lifetime.
+  ObserverList<RenderProcessHostObserver> observers_;
+
   // True if the process can be shut down suddenly.  If this is true, then we're
   // sure that all the RenderViews in the process can be shutdown suddenly.  If
   // it's false, then specific RenderViews might still be allowed to be shutdown