This is a reland of e72789f5

Original change's description:
> win toolchain: Prepare downloader for windows sdk dir switch
>
> crrev.com/c/2655836 tries to move the Windows SDK from
> "win_sdk" to "Windows Kits/10".
>
> get_toolchain_if_necessary.py (in depot_tools) saves the path to the SDK to
> third_party/depot_tools/win_toolchain/data.json which then gets copied
> by a script in the chromium repo to build/win_toolchain.json.
> For the SDK move to work, chromium's pinned depot_tools
> must write the new SDK path when rolling in the new toolchain package.
> This change makes depot_tools handle win packages that have the
> windows sdk either win "win_sdk" or in "Windows Kits\10".
>
> The plan is:
>
> 1. Land this change, which can handle both path styles
> 2. Wait for depot_tools in chromium to update
> 3. Then roll to a win toolchain package with the new layout
>
> In a few years, when we no longer need the old layout,
> we can remove this detection code again and assume the new layout.
>
> Bug: 1173176
> Change-Id: Iaefc5c16685d3dbfff87a3e50a7b20b457366e44
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2666429
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Auto-Submit: Nico Weber <thakis@chromium.org>
> Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

Bug: 1173176,1173393
Change-Id: Ic706f694f8f0260208fa637864e62d7cc4f7ce93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2668127
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>