Files.app: Re-implement the notifications for removable devices in JavaScript.

Currently the notifications for removable devices are implemented in C++. But
now we have the extension notification API, so we can implement thme in
JavaScript.

This CL adds an event of device state change to the file manager private API,
and handles it to show the notifications.

BUG=330096
TEST=insert USB on link

Review URL: https://codereview.chromium.org/113893008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243076 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243076