Make GetDisplayedNotifications asynchronous.

chrome/browser/notifications/notification_platform_bridge.h

Index: chrome/browser/notifications/notification_platform_bridge.h
diff --git a/chrome/browser/notifications/notification_platform_bridge.h b/chrome/browser/notifications/notification_platform_bridge.h
index 720245c8c8eb12465b5ab9d6d5ed949b4daa636f..231a0fd35094f85f9850eaebdb2c60f220f54ad8 100644
--- a/chrome/browser/notifications/notification_platform_bridge.h
+++ b/chrome/browser/notifications/notification_platform_bridge.h
@@ -8,6 +8,7 @@
 #include <set>
 #include <string>
 
+#include "base/callback_forward.h"
 #include "base/macros.h"
 #include "chrome/browser/notifications/notification_common.h"
 
@@ -19,6 +20,10 @@ class Notification;
 // TODO(miguelg): Add support for click and close events.
 class NotificationPlatformBridge {
  public:
+  using DisplayedNotificationsCallback =
+      base::Callback<void(std::unique_ptr<std::set<std::string>>,
+                          bool /* supports_synchronization */)>;
+
   static NotificationPlatformBridge* Create();
 
   virtual ~NotificationPlatformBridge() {}
@@ -35,14 +40,12 @@ class NotificationPlatformBridge {
   virtual void Close(const std::string& profile_id,
                      const std::string& notification_id) = 0;
 
-  // Fills in |notifications| with a set of notification ids currently being
-  // displayed for a given profile.
-  // The return value expresses whether the underlying platform has the
-  // capability to provide displayed notifications so the empty set
-  // can be disambiguated.
-  virtual bool GetDisplayed(const std::string& profile_id,
-                            bool incognito,
-                            std::set<std::string>* notification_ids) const = 0;
+  // Writes the ids of all currently displaying notifications and posts
+  // |callback| with the result.
+  virtual void GetDisplayed(
+      const std::string& profile_id,
+      bool incognito,
+      const DisplayedNotificationsCallback& callback) const = 0;
 
  protected:
   NotificationPlatformBridge() {}