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This reverts commit 12dca865.

Reason for revert: crbug.com/795223

Original change's description:
> Fix Windows touchpad lagging in first tab
>
> Currently the receiving of WM_MOUSEWHEEL messages lags when we open a
> URL on a new window until we resize. The issue was introduced by
> r384698. That CL change wait for MOUSE_EVENT to wait for SENDMESSAGE
> in MessagePumpForUI::WaitForWork to optimize the GPU thread. But the
> GPU thread does not use MessagePumpForUI anymore so it should be OK to
> just remove that code.
>
> The updated version of Chrome was tested to make sure that the hangs
> that were occasionally seen when using chrome://tracing are still gone.
>
> After this CL chaopeng@ need to monitor to make sure that the crash
> rate not increase.
>
> Bug: 713907, 596190
> Change-Id: I7545a867de4851acd4e57c9b8c7a3dd05def1dd8
> Reviewed-on: https://chromium-review.googlesource.com/809829
> Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
> Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#523689}

TBR=thestig@chromium.org,brucedawson@chromium.org,chaopeng@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 713907, 596190, 795223
Change-Id: I3f53fd77e7a6545cd214444cac46709cff0142c9
Reviewed-on: https://chromium-review.googlesource.com/830174
Commit-Queue: Jianpeng Chao <chaopeng@chromium.org>
Reviewed-by: Jianpeng Chao <chaopeng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524428}