Adds a ServerViewObserver interface

services/view_manager/server_view.h

Index: services/view_manager/server_view.h
diff --git a/services/view_manager/server_view.h b/services/view_manager/server_view.h
index 03842e7bb5cfc0a3db9231bf362fd22fafb14f9a..f0050a42620023166978eb8e8fe66e1190c44c48 100644
--- a/services/view_manager/server_view.h
+++ b/services/view_manager/server_view.h
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/logging.h"
+#include "base/observer_list.h"
 #include "cc/surfaces/surface_id.h"
 #include "mojo/services/view_manager/public/interfaces/view_manager.mojom.h"
 #include "services/view_manager/ids.h"
@@ -17,6 +18,7 @@
 namespace view_manager {
 
 class ServerViewDelegate;
+class ServerViewObserver;
 
 // Server side representation of a view. Delegate is informed of interesting
 // events.
@@ -29,6 +31,9 @@ class ServerView {
   ServerView(ServerViewDelegate* delegate, const ViewId& id);
   virtual ~ServerView();
 
+  void AddObserver(ServerViewObserver* observer);
+  void RemoveObserver(ServerViewObserver* observer);
+
   const ViewId& id() const { return id_; }
 
   void Add(ServerView* child);
@@ -101,6 +106,8 @@ class ServerView {
 
   std::map<std::string, std::vector<uint8_t>> properties_;
 
+  ObserverList<ServerViewObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(ServerView);
 };