[tools] Add VPython config for callstats.py

TBR=machenbach@chromium.org

Bug: chromium:861668
Change-Id: I099b2ff007bed8b35e13d7f52eb5d0ae390a230e
Reviewed-on: https://chromium-review.googlesource.com/1174267
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55117}

.vpython

 # This is a vpython "spec" file.
 #
 # It describes patterns for python wheel dependencies of the python scripts in
-# the chromium repo, particularly for dependencies that have compiled components
+# the V8 repo, particularly for dependencies that have compiled components
 # (since pure-python dependencies can be easily vendored into third_party).
 #
 # When vpython is invoked, it finds this file and builds a python VirtualEnv,

tools/callstats.py.vpython

+# This is a vpython "spec" file.
+#
+# It describes patterns for python wheel dependencies of the python scripts in
+# the callstats.py, particularly for dependencies that have compiled components
+# (since pure-python dependencies can be easily vendored into third_party).
+#
+# When vpython is invoked, it finds this file and builds a python VirtualEnv,
+# containing all of the dependencies described in this file, fetching them from
+# CIPD (the "Chrome Infrastructure Package Deployer" service). Unlike `pip`,
+# this never requires the end-user machine to have a working python extension
+# compilation environment. All of these packages are built using:
+#   https://chromium.googlesource.com/infra/infra/+/master/infra/tools/dockerbuild/
+#
+# All python scripts in the repo share this same spec, to avoid dependency
+# fragmentation.
+#
+# If you have depot_tools installed in your $PATH, you can invoke python scripts
+# in this repo by running them as you normally would run them, except
+# substituting `vpython` instead of `python` on the command line, e.g.:
+#   vpython path/to/script.py some --arguments
+#
+# Read more about `vpython` and how to modify this file here:
+#   https://chromium.googlesource.com/infra/infra/+/master/doc/users/vpython.md
+
+python_version: "2.7"
+
+wheel: <
+  name: "infra/python/wheels/numpy/${vpython_platform}"
+  version: "version:1.11.3"
+>