vs_toolchain.py: Add default path for MSVS 2017 Enterprise.

bertholdherrmann08@googlemail.com reported this issue for WebRTC
and it seems easy to just add
r'C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise'
to the predefined paths.

BUG=webrtc:8299

Change-Id: I3bec73e2ef48e1a2b7e05a4df38faed2efc5ebfc
Reviewed-on: https://chromium-review.googlesource.com/691730
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Henrik Kjellander <kjellander@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#505419}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 84e6c2d657fc4b56d6736eaacae55342058729c1

vs_toolchain.py

@@ -153,6 +153,7 @@ def DetectVisualStudioPath():
     # For now we use a hardcoded default with an environment variable override.
     for path in (
         os.environ.get('vs2017_install'),
+        r'C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise',
         r'C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional',
         r'C:\Program Files (x86)\Microsoft Visual Studio\2017\Community'):
       if path and os.path.exists(path):