Export a private webstore API to call into the new inline sign-in flow.

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 27d0c3f98659bb8bc7901b9e97e038e26e5fb146..8c72c33e9b99f153263f285b150889b9a6a3cd43 100644
--- a/components/signin/core/browser/signin_manager.h
+++ b/components/signin/core/browser/signin_manager.h
@@ -129,8 +129,10 @@ class SigninManager : public SigninManagerBase {
   bool IsSignoutProhibited() const;
 
   // Add or remove observers for the merge session notification.
-  void AddMergeSessionObserver(MergeSessionHelper::Observer* observer);
-  void RemoveMergeSessionObserver(MergeSessionHelper::Observer* observer);
+  virtual void AddMergeSessionObserver(
+      MergeSessionHelper::Observer* observer);
+  virtual void RemoveMergeSessionObserver(
+      MergeSessionHelper::Observer* observer);
 
  protected:
   // Flag saying whether signing out is allowed.