Preliminary changes to git cl and presubmit_support

Added an rdb wrapper and use it to time CheckChangeOn{Commit, Upload} from every PRESUBMIT.py file, then reports the results to ResultSink.

Bug: http://crbug.com/1107588

Change-Id: I9bc8a18ba615a76f3e0611eae5b2c4adc5924276
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2242097
Commit-Queue: Saagar Sanghavi <saagarsanghavi@google.com>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>

rdb_wrapper.py

@@ -0,0 +1,65 @@
+#!/usr/bin/env vpython
+# Copyright (c) 2020 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import contextlib
+import json
+import os
+import requests
+import time
+
+# Constants describing TestStatus for ResultDB
+STATUS_PASS = 'PASS'
+STATUS_FAIL = 'FAIL'
+STATUS_CRASH = 'CRASH'
+STATUS_ABORT = 'ABORT'
+STATUS_SKIP = 'SKIP'
+
+class ResultSinkStatus(object):
+  def __init__(self):
+    self.status = STATUS_PASS
+
+@contextlib.contextmanager
+def setup_rdb(function_name, rel_path):
+  """Context Manager function for ResultDB reporting.
+
+  Args:
+    function_name (str): The name of the function we are about to run.
+    rel_path (str): The relative path from the root of the repository to the
+      directory defining the check being executed.
+  """
+  sink = None
+  if 'LUCI_CONTEXT' in os.environ:
+    with open(os.environ['LUCI_CONTEXT']) as f:
+      j = json.load(f)
+      if 'result_sink' in j:
+        sink = j['result_sink']
+
+  my_status = ResultSinkStatus()
+  start_time = time.time()
+  try:
+    yield my_status
+  except Exception:
+    my_status.status = STATUS_FAIL
+    raise
+  finally:
+    end_time = time.time()
+    elapsed_time = end_time - start_time
+    if sink != None:
+      tr = {
+          'testId': '{0}/:{1}'.format(rel_path, function_name),
+          'status': my_status.status,
+          'expected': (my_status.status == STATUS_PASS),
+          'duration': '{:.9f}s'.format(elapsed_time)
+      }
+      requests.post(
+          url='http://{0}/prpc/luci.resultsink.v1.Sink/ReportTestResults'
+                  .format(sink['address']),
+          headers={
+            'Content-Type': 'application/json',
+            'Accept': 'application/json',
+            'Authorization': 'ResultSink {0}'.format(sink['auth_token'])
+          },
+          data=json.dumps({'testResults': [tr]})
+    )