Add metrics_python_tests runner and run it on the bots.

Also contains a couple of fixes for the tests included
in the new runner so that they pass properly when invoked
in this new way.

Bug: 757504
Change-Id: If2d5045f67f416ac0dd902833d5e5d16029f3105
Reviewed-on: https://chromium-review.googlesource.com/701499
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: Alexei Svitkine <[email protected]>
Cr-Commit-Position: refs/heads/master@{#507047}
diff --git a/testing/buildbot/gn_isolate_map.pyl b/testing/buildbot/gn_isolate_map.pyl
index e76223c4..04f67581 100644
--- a/testing/buildbot/gn_isolate_map.pyl
+++ b/testing/buildbot/gn_isolate_map.pyl
@@ -762,6 +762,14 @@
     "label": "//ui/message_center:message_center_unittests",
     "type": "windowed_test_launcher",
   },
+  "metrics_python_tests": {
+    "label": "//tools/metrics:metrics_python_tests",
+    "type": "script",
+    "script": "//testing/scripts/run_isolated_script_test.py",
+    "args": [
+      "../../tools/metrics/metrics_python_tests.py"
+    ]
+  },
   "mash_unittests": {
     "label": "//mash:mash_unittests",
     "type": "windowed_test_launcher",