[epiphany] (8 commits) ...WebExtensions: Implement getting return value for tabs.executeScript()

[Marge Bot <marge-bot src gnome org>]

Summary of changes:

  4228d3f... ephy_shell_new_tab_full: Support NULL window (*)
  71bca8c... WebExtensions: Stub out tabs events (*)
  c7d79ee... WebExtensions: Implement tabs.create() (*)
  9d42e89... WebExtensions: Implement tabs.remove() (*)
  9eaf507... WebExtensions: Implement tabs.getZoom() and tabs.setZoom() (*)
  e978210... WebExtensions: Implement tabs.getCurrent() (*)
  5c210f4... WebExtensions: Implement tabs.update() (*)
  9f3f40d... WebExtensions: Implement getting return value for tabs.exec (*)

(*) This commit already existed in another branch; no separate mail sent