[FS Shortcut] Do not start hold timer for Esc + [modifier key]

When the Esc key is pressed down with other modifier keys (i.e. Shift,
Cmd), the Esc key up event might not be sent to the browser. As a
result, the browser does not know the Esc key is released and might
exit the browser fullscreen or unlock the keyboard lock.

This CL makes the change so that the hold timer is only started when
the Esc key is pressed down without modifier keys.

Bug: 345312747
Change-Id: Ifdee8f3b64cb1b3bd363a16e03e6e8e09e49e13e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5610312


Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Commit-Queue: Muyao Xu <muyaoxu@google.com>
Cr-Commit-Position: refs/heads/main@{#1313131}