athena: Use ActivityList where appropriate, and fix AppActivity tests.

athena/activity/public/activity_manager.h

Index: athena/activity/public/activity_manager.h
diff --git a/athena/activity/public/activity_manager.h b/athena/activity/public/activity_manager.h
index 3453fa96cb72e236bfe63db984bbafe44011d44c..9c6bff97381c75304ee556e866645b0930967e24 100644
--- a/athena/activity/public/activity_manager.h
+++ b/athena/activity/public/activity_manager.h
@@ -7,7 +7,9 @@
 
 #include <vector>
 
+#include "athena/activity/public/activity.h"
 #include "athena/athena_export.h"
+#include "base/memory/scoped_ptr.h"
 
 namespace aura {
 class Window;
@@ -18,7 +20,14 @@ namespace athena {
 class Activity;
 class ActivityManagerObserver;
 
+struct ActivityDeleter {
+  inline void operator()(Activity* activity) const {
+    Activity::Delete(activity);
+  }
+};
+
 using ActivityList = std::vector<Activity*>;
+using ScopedActivity = scoped_ptr<Activity, ActivityDeleter>;
 
 // Manages a set of activities.
 class ATHENA_EXPORT ActivityManager {
@@ -33,6 +42,9 @@ class ATHENA_EXPORT ActivityManager {
   virtual void AddActivity(Activity* activity) = 0;
   virtual void RemoveActivity(Activity* activity) = 0;
 
+  virtual ScopedActivity ReplaceActivity(Activity* to_replace,
+                                         Activity* replace_with) = 0;
+
   // Returns a list of activities, sorted in their activation order (the most
   // recently used activity is at the front of the returned list).
   virtual const ActivityList& GetActivityList() = 0;