Add UWP support to Windows toolchain.

Slight update to MSVC - VS version from 16.3.1 to 16.4.3 as a side effect.
Other components kept at the old versions:
Windows SDK 10.0.18362
Debuggers 10.0.17763
d3dcompiler_47.dll 10.0.17134

Packaging was done on a Windows Server 2019 VM, cleanly created for this
purpose.

The package was created by downloading VS Professional 2019 installer
from https://visualstudio.microsoft.com/downloads/
and then running the installer like this:

$ PATH_TO_INSTALLER.EXE ^
    --add Microsoft.VisualStudio.Workload.NativeDesktop ^
    --add Microsoft.VisualStudio.Component.VC.ATLMFC ^
    --add Microsoft.VisualStudio.Component.VC.Tools.ARM64 ^
    --add Microsoft.VisualStudio.Component.VC.MFC.ARM64 ^
    --includeRecommended --passive

The 10.0.18362.0 SDK was installed by this as well.
Then Add or Remove Programs was used to modify the 10.0.18362.0 SDK to add
the Debuggers package.

Then the packaging script was run like this:

  python depot_tools\win_toolchain\package_from_installed.py 2019 -w 10.0.18362.0

Since the new d3dcompiler_47.dll uses the UCRT and we want to avoid shipping
that the final packaging step was to unzip the package, copy over the two copies
of that DLL from win_sdk\Redist, replace the Debuggers directory with the
10.0.17763 SDK, and then repackage the toolchain with:
  > python package_from_installed.py --repackage=<full-path-to-toolchain-dir>

UWP support was previously added to package_from_installed.py
in http://crrev.com/c/2007881 and http://crrev.com/c/2013579

Bug: 1032635
Change-Id: I85313de0529aa7591e5066bc697c640c5dc52463
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015984Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734608}

build/vs_toolchain.py

@@ -423,12 +423,13 @@ def _GetDesiredVsToolchainHashes():
   * //docs/windows_build_instructions.md mentions of VS or Windows SDK.
     Keeps the document consistent with the toolchain version.
   """
-  # VS 2019 Update 9 (16.3.29324.140) with 10.0.18362 SDK, 10.0.17763 version of
-  # Debuggers, and 10.0.17134 version of d3dcompiler_47.dll, with ARM64
-  # libraries.
+  # VS 2019 version 16.4.3 (16.4.29709.97) with 10.0.18362 SDK,
+  # 10.0.17763 version of Debuggers,
+  # and 10.0.17134 version of d3dcompiler_47.dll,
+  # with ARM64 libraries and UWP support.
   # See go/chromium-msvc-toolchain for instructions about how to update the
   # toolchain.
-  toolchain_hash = '8f58c55897a3282ed617055775a77ec3db771b88'
+  toolchain_hash = 'b92fff97f2e0323e99803f37f4b77b843bdbf69d'
   # Third parties that do not have access to the canonical toolchain can map
   # canonical toolchain version to their own toolchain versions.
   toolchain_hash_mapping_key = 'GYP_MSVS_HASH_%s' % toolchain_hash