Fix a Python3-compatibility issue in get_toolchain_if_necessary.

Bug: 1207012
Change-Id: I9205089c3a7d9f2d3e2eb9aac7ef6da9ae9b0876
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2890330
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>

win_toolchain/get_toolchain_if_necessary.py

@@ -560,7 +560,7 @@ def main():
   version_file = os.path.join(toolchain_target_dir, 'VS_VERSION')
   vc_dir = os.path.join(toolchain_target_dir, 'VC')
   with open(version_file, 'rb') as f:
-    vs_version = f.read().strip()
+    vs_version = f.read().decode('utf-8').strip()
     # Touch the VC directory so we can use its timestamp to know when this
     # version of the toolchain has been used for the last time.
   os.utime(vc_dir, None)