Revert of Make File-Picker modal on Linux (patchset #8 id:140001 of

Reason for revert:
This patch causes DCHECK failure. Refer to:

Original issue's description:
> Make File-Picker modal on Linux
> Chromium for Linux opens a Gtk file-picker for file browsing, but it is not
> modal because there is no GtkWindow as parent of file-picker.
> This patch allows the X11 host window to disable input event handling to make
> a file-picker modal.
> BUG=408481
> Committed:
> Cr-Commit-Position: refs/heads/master@{#338870}


Review URL:

Cr-Commit-Position: refs/heads/master@{#339173}
4 files changed