Chrome extension executescript into external drive file - google-chrome

Question

I have created an extension that uses the executescript api to inject a piece of code (shown below) that basically on window.onbeforeunload confirms they want to close the page. I have the script working, and by using the file://*/* permission, got it to inject on file URLs. However, when testing it on a flash game I downloaded, the script didn't inject. The URL was externalfile:drive-randomtext/root/SWFNAME.swf. I tried adding externalfile://*/* in the permissions but got the following error message: There were warnings when trying to install this extension: Permission 'externalfile://*/*' is unknown or URL pattern is malformed. Is there an external file permission, or another way to do this?
Manifest.json:
{
"name": "name",
"short_name": "name",
"version": "3.6",
"manifest_version": 2,
"description": "Desc",
"permissions": [
"storage",
"http://*/",
"https://*/",
"tabs",
"activeTab",
"webNavigation",
"*://*/*",
"file://*/*"
],
"page_action": {
"default_icon": "logo.png"
},
"background": {
"scripts": ["disabled.js"]
}
}
Script that gets executed:
(hotkey-binding code too long, can be found here)
Mousetrap.bind('ctrl+m', function(e) {
window.onbeforeunload = confirmExit;function confirmExit(){alert('confirm exit is being called');return'Close page?';}
alert('Enabled');
return false;
});
Mousetrap.bind('ctrl+q', function(e) {
location.reload();
return false;
});