Adds a webstorePrivate method for silently installing extensions.

chrome/browser/extensions/webstore_installer.h

Index: chrome/browser/extensions/webstore_installer.h
diff --git a/chrome/browser/extensions/webstore_installer.h b/chrome/browser/extensions/webstore_installer.h
index c8043550f158bd2c5586800b3ff73ee3f63a6333..ef2bbbc52c4a4d22390fa5263bf51103a940a50c 100644
--- a/chrome/browser/extensions/webstore_installer.h
+++ b/chrome/browser/extensions/webstore_installer.h
@@ -15,6 +15,7 @@
 #include "content/public/browser/notification_registrar.h"
 #include "googleurl/src/gurl.h"
 
+class FilePath;
 class NavigationController;
 class Profile;
 
@@ -60,6 +61,9 @@ class WebstoreInstaller : public content::NotificationObserver,
                        const content::NotificationDetails& details) OVERRIDE;
 
  private:
+  // Starts downloading the extension to |file_path|.
+  void StartDownload(FilePath file_path);
+
   // Reports an install |error| to the delegate for the given extension if this
   // managed its installation. This also removes the associated PendingInstall.
   void ReportFailure(const std::string& error);