athena: Expose the list of activities from the ActivityManager.

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 99d8e75a049fdc1999de56c629403bf364430806..4eadf87bac8727f195d3c93bf1e2aae0bf846472 100644
--- a/athena/activity/public/activity_manager.h
+++ b/athena/activity/public/activity_manager.h
@@ -5,6 +5,8 @@
 #ifndef ATHENA_ACTIVITY_PUBLIC_ACTIVITY_MANAGER_H_
 #define ATHENA_ACTIVITY_PUBLIC_ACTIVITY_MANAGER_H_
 
+#include <vector>
+
 #include "athena/athena_export.h"
 
 namespace aura {
@@ -16,6 +18,8 @@ namespace athena {
 class Activity;
 class ActivityManagerObserver;
 
+using ActivityList = std::vector<Activity*>;
+
 // Manages a set of activities.
 class ATHENA_EXPORT ActivityManager {
  public:
@@ -29,13 +33,17 @@ class ATHENA_EXPORT ActivityManager {
   virtual void AddActivity(Activity* activity) = 0;
   virtual void RemoveActivity(Activity* activity) = 0;
 
+  // Updates the UI when the task color/title changes.
+  virtual void UpdateActivity(Activity* activity) = 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;
+
   // Returns the activity that has a |window| as toplevel window, or
   // nullptr if such activity does not exist.
   virtual Activity* GetActivityForWindow(aura::Window* window) = 0;
 
-  // Updates the UI when the task color/title changes.
-  virtual void UpdateActivity(Activity* activity) = 0;
-
   virtual void AddObserver(ActivityManagerObserver* observer) = 0;
   virtual void RemoveObserver(ActivityManagerObserver* observer) = 0;
 };