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This is a reland of 13143b64ae10001dd25dcb8b2d8e707b9e439382

Original change's description:
> [Settings] UserEvents depends on history and passphrase
>
> The user events UI toggle should be grayed out and turned off
> when there is a passphrase or when history sync is disabled.
> Note that this is purely a UI change: the internal sync datatype
> is not really turned off in that case, and we assume that the Sync
> engines will correctly stop syncing user events in these cases,
> even if the preference is still ON.
>
> Bug: 865522, 865537
> Change-Id: I04844e2ab9c631300e88f02bbedd712f7618bc32
> Reviewed-on: https://chromium-review.googlesource.com/1160658
> Reviewed-by: Scott Chen <scottchen@chromium.org>

TBR=droger

Bug: 865522, 865537
Change-Id: Ifae79eaf00a42c3b536bc54fa5d23cbcbcabd18a
Reviewed-on: https://chromium-review.googlesource.com/1170202
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582078}