SigninManager owns ObserverList for the MergeSessionHelper.

components/signin/core/browser/signin_manager.h

Index: components/signin/core/browser/signin_manager.h
diff --git a/components/signin/core/browser/signin_manager.h b/components/signin/core/browser/signin_manager.h
index 4ba0ef05bb00d83aeeb5096c387d8845e3f4d1d1..f8f9f2a0fe55ffa8fad23d3f39e8ead83c84cec7 100644
--- a/components/signin/core/browser/signin_manager.h
+++ b/components/signin/core/browser/signin_manager.h
@@ -46,7 +46,8 @@ class SigninAccountIdHelper;
 class SigninClient;
 
 class SigninManager : public SigninManagerBase,
-                      public AccountTrackerService::Observer {
+                      public AccountTrackerService::Observer,
+                      public MergeSessionHelper::Observer {
  public:
   // The callback invoked once the OAuth token has been fetched during signin,
   // but before the profile transitions to the "signed-in" state. This allows
@@ -178,6 +179,13 @@ class SigninManager : public SigninManagerBase,
       override;
   void OnAccountUpdateFailed(const std::string& account_id) override;
 
+  // MergeSessionHelper::Observer implementation. SigninManager controls the
+  // lifetime if the MergeSessionHelper, so SigninManager takes responsibility
+  // for propogating these notifications.
+  void MergeSessionCompleted(const std::string& account_id,
+                             const GoogleServiceAuthError& error) override;
+  void GetCheckConnectionInfoCompleted(bool succeeded) override;
+
   // Called when a new request to re-authenticate a user is in progress.
   // Will clear in memory data but leaves the db as such so when the browser
   // restarts we can use the old token(which might throw a password error).
@@ -229,6 +237,9 @@ class SigninManager : public SigninManagerBase,
   // Helper to merge signed in account into the content area.
   scoped_ptr<MergeSessionHelper> merge_session_helper_;
 
+  // Observers of the |merge_session_helper_| across reset()s.
+  ObserverList<MergeSessionHelper::Observer, true> merge_session_observer_list_;
+
   // Two gate conditions for when PostSignedIn should be called. Verify
   // that the SigninManager has reached OnSignedIn() and the AccountTracker
   // has completed calling GetUserInfo.