Fires at the top of each of the tabs on the Install Themes page.
The dynamic portion of the hook name,
$tab, refers to the current
theme installation tab. Possible values are 'dashboard', 'search', 'upload',
'featured', 'new', or 'updated'.
Related Functions: install_themes_upload, install_themes_dashboard, install_themes_feature_list, install_theme_information, install_theme_search_form, wp_ajax_install_theme