Fix MSVC toolset selection issue

Windows ARM64 build bot is broken on copying runtime dlls.
A recent change switches the MSVC version to VS 2019 as preferred
( https://chromium-review.googlesource.com/c/chromium/src/+/1836195 ).
This affects the search of runtime dlls, since currently VC141
toolset is selected.

As a workaround select the proper toolset directory based on VS version.

Bug: 1013508
Change-Id: Iaebee100be727f60d7bd651202af725abf4726d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1855966Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705633}

build/vs_toolchain.py

@@ -29,6 +29,11 @@ MSVS_VERSIONS = collections.OrderedDict([
   ('2017', '15.0'),
 ])
 
+# List of preferred VC toolset version based on MSVS
+MSVC_TOOLSET_VERSION = {
+   '2019' : 'VC142',
+   '2017' : 'VC141',
+}
 
 def SetEnvironmentAndGetRuntimeDllDirs():
   """Sets up os.environ to use the depot_tools VS toolchain with gyp, and
@@ -241,14 +246,19 @@ def _CopyUCRTRuntime(target_dir, source_dir, target_cpu, dll_pattern, suffix):
   exist, but the target directory does exist."""
   if target_cpu == 'arm64':
     # Windows ARM64 VCRuntime is located at {toolchain_root}/VC/Redist/MSVC/
-    # {x.y.z}/[debug_nonredist/]arm64/Microsoft.VC141.CRT/.
+    # {x.y.z}/[debug_nonredist/]arm64/Microsoft.VC14x.CRT/.
+    # Select VC toolset directory based on Visual Studio version
     vc_redist_root = FindVCRedistRoot()
     if suffix.startswith('.'):
+      vc_toolset_dir = 'Microsoft.{}.CRT' \
+         .format(MSVC_TOOLSET_VERSION[GetVisualStudioVersion()])
       source_dir = os.path.join(vc_redist_root,
-                                'arm64', 'Microsoft.VC141.CRT')
+                                'arm64', vc_toolset_dir)
     else:
+      vc_toolset_dir = 'Microsoft.{}.DebugCRT' \
+         .format(MSVC_TOOLSET_VERSION[GetVisualStudioVersion()])
       source_dir = os.path.join(vc_redist_root, 'debug_nonredist',
-                                'arm64', 'Microsoft.VC141.DebugCRT')
+                                'arm64', vc_toolset_dir)
   for file_part in ('msvcp', 'vccorlib', 'vcruntime'):
     dll = dll_pattern % file_part
     target = os.path.join(target_dir, dll)