Handle webview shortcuts at most once
Handle webview shortcuts at most once

Fix #6796

Auditors: @bridiver

Multiple updates can happen for a shortcut if other state changes, this only seems to happen when pocket is enabled, but the shortcut should only be handled once.

diasdavid/browser-laptop,luixxiul/browser-laptop,darkdh/browser-laptop,darkdh/browser-laptop,diasdavid/browser-laptop,timborden/browser-laptop,darkdh/browser-laptop,timborden/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop,darkdh/browser-laptop,timborden/browser-laptop,luixxiul/browser-laptop,timborden/browser-laptop,diasdavid/browser-laptop,luixxiul/browser-laptop