Add vs_toolchain.py to analyze exclusions.

If //build/vs_toolchain.py is changed (or any file it imports,
including gn_helpers.py), we should bypass `analyze` on the
trybots because we may need to rebuild everything.

(Technically, we only need to do this on Win hosts, but we don't
have a good way of filtering that at the moment).

This is needed when updating the VS toolchain, including SDK updates.
This change makes it so that a full build will be requested. The
build will be a NOP unless the toolchain has actually changed, in which
case the changed command lines will make all of the compile commands
dirty.

Bug: 842111
Change-Id: I2222798c7c8fd691383a0eca1414d1e8afdb55f8
Reviewed-on: https://chromium-review.googlesource.com/1055869Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558342}

testing/buildbot/trybot_analyze_config.json

@@ -18,11 +18,13 @@
       "build/cipd/android/android.ensure",
       "build/fuchsia/.*py",
       "build/get_landmines.py",
+      "build/gn_helpers.py",
       "build/gyp_chromium",
       "build/mac_toolchain.py",
       "build/toolchain/get_concurrent_links.py",
       "build/toolchain/mac/.*py",
       "build/util/lib/common/unittest_util.py",
+      "build/vs_toolchain.py",
       "infra/scripts/.*",
       "DEPS",
       "testing/buildbot/.*json",