Update Win build instructions for VS2019

This updates the windows build instructions to indicate that
Visual Studio 2019 is the preferred VS IDE version, and to
align with the default changing in
https://gn-review.googlesource.com/c/gn/+/6900

Bug: 1038361
No-Try: true
Change-Id: I2a9908f02d7a8dc42e94d330550035554968b4a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1984701
Commit-Queue: Aaron Gable <agable@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727988}

docs/windows_build_instructions.md

@@ -23,8 +23,8 @@ Are you a Google employee? See
 
 ### Visual Studio
 
-Chromium requires Visual Studio 2017 (>=15.7.2) or 2019 (>=16.0.0) to build.
-Visual Studio can also be used to debug Chromium and Visual Studio 2019 is
+Chromium requires Visual Studio 2017 (>=15.7.2) to build, but VS2019 (>=16.0.0)
+is preferred. Visual Studio can also be used to debug Chromium, and VS2019 is
 preferred for this as it handles Chromium's large debug information much better.
 The clang-cl compiler is used but Visual Studio's header files, libraries, and
 some tools are required. Visual Studio Community Edition should work if its
@@ -89,8 +89,8 @@ if your system PATH has a Python in it, you will be out of luck.
 Also, add a DEPOT_TOOLS_WIN_TOOLCHAIN system variable in the same way, and set
 it to 0. This tells depot_tools to use your locally installed version of Visual
 Studio (by default, depot_tools will try to use a google-internal version). If
-you want to build with Visual Studio 2019 instead of Visual Studio 2017 (the
-default) then set the GYP_MSVS_VERSION environment variable to 2019.
+you want to build with Visual Studio 2017 instead of Visual Studio 2019 (the
+default) then set the GYP_MSVS_VERSION environment variable to 2017.
 
 From a cmd.exe shell, run the command gclient (without arguments). On first
 run, gclient will install all the Windows-specific bits needed to work with