Revert "Reland "Removes ui/platform_window/mojo as it is not used by anyone.""

This reverts commit 6700540dcbab00b4120fa39b41ea51d4c5fc3a3b.

Reason for revert: Win x64 Builder failure!
https://ci.chromium.org/p/chromium/builders/ci/Win%20x64%20Builder%20%28dbg%29/90510

Original change's description:
> Reland "Removes ui/platform_window/mojo as it is not used by anyone."
> 
> This is a reland of 6eb61402c1b1b4301762c6aaaea28b2921cbf4c2
> 
> Original change's description:
> > Removes ui/platform_window/mojo as it is not used by anyone.
> > 
> > This is to remove the ref to some types under ui/base/ime/mojo, which will be removed later.
> > 
> > Bug: 965908
> > Change-Id: I7979524066104c829b4f4e287a0ab87c9365f124
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626055
> > Reviewed-by: Dominick Ng <dominickn@chromium.org>
> > Reviewed-by: Scott Violet <sky@chromium.org>
> > Commit-Queue: Shu Chen <shuchen@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#662924}
> 
> Bug: 965908
> Change-Id: I6bb1c6d081ce235c959cc30e53d20b57dd0e1459
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626841
> Reviewed-by: Dominick Ng <dominickn@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Shu Chen <shuchen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#663381}

TBR=sky@chromium.org,shuchen@chromium.org,dominickn@chromium.org

Change-Id: I1649ad44813f8de696a3b5f651515a9145f478bd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 965908
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1630127
Reviewed-by: Shu Chen <shuchen@chromium.org>
Commit-Queue: Shu Chen <shuchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663384}
12 files changed