Adds a webstorePrivate method for silently installing extensions.

chrome/browser/extensions/crx_installer.h

Index: chrome/browser/extensions/crx_installer.h
diff --git a/chrome/browser/extensions/crx_installer.h b/chrome/browser/extensions/crx_installer.h
index d2955ae9b5ae4f494e0a19287dfb9c999fa1b9bd..4938388b53bb86b1f140e5e86cf25add6f13298d 100644
--- a/chrome/browser/extensions/crx_installer.h
+++ b/chrome/browser/extensions/crx_installer.h
@@ -75,6 +75,9 @@ class CrxInstaller
     // Whether to use a bubble notification when an app is installed, instead of
     // the default behavior of transitioning to the new tab page.
     bool use_app_installed_bubble;
+
+    // Whether to skip the post install UI like the extension installed bubble.
+    bool skip_post_install_ui;
   };
 
   // Exempt the next extension install with |id| from displaying a confirmation