Revert of Make File-Picker modal on Linux (patchset #8 id:140001 of https://codereview.chromium.org/1045443002/)

Reason for revert:
This patch causes DCHECK failure. Refer to:
https://code.google.com/p/chromium/issues/detail?id=510957

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: https://crrev.com/b440cbb929e62a238f97590d79bd78333adef7ce
> Cr-Commit-Position: refs/heads/master@{#338870}

BUG=408481,510957

Review URL: https://codereview.chromium.org/1243503002

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