Get v8 builds to use up-to-date VS toolchains

The VS 2013 toolchain used by v8 is ~two months out of date. The
Chromium toolchain was updated in October to include the Windows 10
SDK. Using a different toolchain in v8 leads to the possibility of
odd incompatibilities, and means that switching between Chromium and
v8 requires a time-consuming reinstallation of the toolchain. The
VS 2013 toolchain was updated by crrev.com/1502563003.

The VS 2015 toolchain used by v8 is also out of date. It is the wrong
compiler version (RTM instead of Update 1), the wrong SDK version, and
it is missing files such as the UCRT installers.

LOG=N
BUG=440500,491424

Review URL: https://codereview.chromium.org/1632363002

Cr-Commit-Position: refs/heads/master@{#33560}

build/vs_toolchain.py

@@ -191,10 +191,10 @@ def _GetDesiredVsToolchainHashes():
   """Load a list of SHA1s corresponding to the toolchains that we want installed
   to build with."""
   if os.environ.get('GYP_MSVS_VERSION') == '2015':
-    return ['49ae4b60d898182fc3f521c2fcda82c453915011']
+    return ['5a85cf1ce842f7cc96b9d17039a445a9dc9cf0dd']
   else:
     # Default to VS2013.
-    return ['ee7d718ec60c2dc5d255bbe325909c2021a7efef']
+    return ['9ff97c632ae1fee0c98bcd53e71770eb3a0d8deb']
 
 
 def Update(force=False):