Add coverage library to vpython3 so that we can have better insight in how we stand wrt our test coverage in depot_tools.

Bug: b/459690822
Change-Id: I17d67e0530755fa9c07bbc4dabf6d81b6a6a6964
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/7244730
Auto-Submit: Alex Ovsienko <ovsienko@google.com>
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Commit-Queue: Alex Ovsienko <ovsienko@google.com>

.gitignore

@@ -99,3 +99,7 @@ testing_support/google_appengine
 
 # Ignore gemini-cli configs
 /.gemini/
+
+# Ignore coverage results file and htlp folder.
+.coverage
+htmlcov/

.vpython3

@@ -102,3 +102,9 @@ wheel: <
   name: "infra/python/wheels/lxml/${vpython_platform}"
   version: "version:4.9.3"
 >
+
+# To be used by developers running unit test coverage.
+wheel: <
+  name: "infra/python/wheels/coverage-py3"
+  version: "version:7.13.0"
+>

pyproject.toml

@@ -2,3 +2,6 @@
 venvPath = 'recipes/.recipe_deps/_venv'
 venv = 'normal'
 extraPaths = ['recipes/.recipe_deps/_path']
+
+[tool.coverage.run]
+disable_warnings = ["no-ctracer"]