Add coverage

tools/telemetry/third_party/coverage/metacov.ini

+# Licensed under the Apache License: http://www.apache.org/licenses/LICENSE-2.0
+# For details: https://bitbucket.org/ned/coveragepy/src/default/NOTICE.txt
+
+# Settings to use when using coverage.py to measure itself.
+[run]
+branch = true
+data_file = $COVERAGE_METAFILE
+parallel = true
+source =
+    $COVERAGE_HOME/coverage
+    $COVERAGE_HOME/tests
+
+[report]
+# We set a different pragma so our code won't be confused with test code.
+exclude_lines =
+    # pragma: not covered
+    # pragma: nested
+    def __repr__
+    raise AssertionError
+    # pragma: debugging
+    # pragma: only failure
+
+partial_branches =
+    # pragma: part covered
+    if env.TESTING:
+
+ignore_errors = true
+precision = 1
+
+[paths]
+source =
+    .
+    *\coverage\trunk
+    */coverage/trunk
+    *\coveragepy