Revert "Mac: do not enable file upload until selection has changed"

This reverts commit 64ef541aad859cc5be38da44863fb1ea24c7c817.

Reason for revert:
(1) The CL fixes the webkitdirectory bug but breaks the normal
<input type=file> upload dialog.
(2) Can fix tapted's nits posted after submit.

Original change's description:
> Mac: do not enable file upload until selection has changed
> 
> To avoid files being uploaded without the user realizing, require the
> user to change the selection on the file dialog before the OK button
> is enabled.
> 
> Bug: 637098
> Change-Id: Ic6faffb3f6075fb969ae930992d2553162346d02
> Reviewed-on: https://chromium-review.googlesource.com/833399
> Reviewed-by: ccameron <ccameron@chromium.org>
> Commit-Queue: Emily Stark <estark@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#525148}

TBR=tapted@chromium.org,ccameron@chromium.org,estark@chromium.org

Change-Id: I885af00fff4f2a20b8a59e8c0dbc8e9f4b4a06fa
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 637098
Reviewed-on: https://chromium-review.googlesource.com/835208
Reviewed-by: Emily Stark <estark@chromium.org>
Commit-Queue: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525166}
1 file changed