Surface cross-browsers failures from a chromium export to its corresponding CL.

Design doc:
https://docs.google.com/document/d/1MtdbUcWBDZyvmV0FOdsTWw_Jv16YtE6KW5BnnCVYX4c/edit#heading=h.7nki9mck5t64

Running Command:
python third_party/blink/tools/wpt_export.py --dry-run --credentials <your credentials> --surface-failures-to-gerrit

Tested on a mock CL
https://chromium-review.googlesource.com/c/chromium/src/+/1784803

Change-Id: I368d6fc5b0f7f3e5364fca1fe26cef3514585f96
Bug: 996383
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1749720
Commit-Queue: Kyle Ju <kyleju@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715167}

third_party/blink/tools/blinkpy/w3c/export_notifier.py

+# Copyright 2019 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.
+
+"""Sends notifications after automatic exports.
+
+Automatically comments on a Gerrit CL when its corresponding PR fails the Taskcluster check. In
+other words, surfaces cross-browser WPT regressions from Github to Gerrit.
+
+
+Design doc: https://docs.google.com/document/d/1MtdbUcWBDZyvmV0FOdsTWw_Jv16YtE6KW5BnnCVYX4c
+
+"""
+
+import logging
+
+from blinkpy.w3c.common import WPT_REVISION_FOOTER
+from blinkpy.w3c.gerrit import GerritError
+from blinkpy.w3c.wpt_github import GitHubError
+
+_log = logging.getLogger(__name__)
+
+
+class ExportNotifier(object):
+
+    def __init__(self, host, wpt_github, gerrit, dry_run=True):
+        self.host = host
+        self.wpt_github = wpt_github
+        self.gerrit = gerrit
+        self.dry_run = dry_run
+
+    def main(self):
+        """Surfaces stability check failures to Gerrit through comments."""
+        gerrit_dict = {}
+
+        try:
+            _log.info('Searching for recent failiing chromium exports.')
+            prs = self.wpt_github.recent_failing_chromium_exports()
+        except GitHubError as e:
+            _log.info(
+                'Surfacing Taskcluster failures cannot be completed due to the following error:')
+            _log.error(str(e))
+            return True
+
+        if len(prs) > 100:
+            _log.error(
+                'Too many open failing PRs: %s; abort.', len(prs))
+            return True
+
+        _log.info('Found %d failing PRs.', len(prs))
+        for pr in prs:
+            statuses = self.get_taskcluster_statuses(pr.number)
+            if not statuses:
+                continue
+
+            taskcluster_status = self.get_failure_taskcluster_status(
+                statuses, pr.number)
+            if not taskcluster_status:
+                continue
+
+            gerrit_id = self.wpt_github.extract_metadata(
+                'Change-Id: ', pr.body)
+            if not gerrit_id:
+                _log.error(
+                    'Can not retrieve Change-Id for %s.', pr.number)
+                continue
+
+            gerrit_sha = self.wpt_github.extract_metadata(
+                WPT_REVISION_FOOTER + ' ', pr.body)
+            gerrit_dict[gerrit_id] = PRStatusInfo(
+                taskcluster_status['node_id'],
+                taskcluster_status['target_url'],
+                gerrit_sha)
+
+        self.process_failing_prs(gerrit_dict)
+        return False
+
+    def get_taskcluster_statuses(self, number):
+        """Retrieves Taskcluster status through PR number.
+
+        Returns:
+            A JSON object representing all Taskcluster statuses for this PR.
+        """
+        try:
+            branch = self.wpt_github.get_pr_branch(number)
+            statuses = self.wpt_github.get_branch_statuses(branch)
+        except GitHubError as e:
+            _log.error(str(e))
+            return None
+
+        return statuses
+
+    def process_failing_prs(self, gerrit_dict):
+        """Processes and comments on CLs with failed TackCluster status."""
+        _log.info('Processing %d CLs with failed Taskcluster status.',
+                  len(gerrit_dict))
+        for change_id, pr_status_info in gerrit_dict.items():
+            try:
+                cl = self.gerrit.query_cl_comments_and_revisions(change_id)
+                has_commented = self.has_latest_taskcluster_status_commented(
+                    cl.messages, pr_status_info)
+                if has_commented:
+                    continue
+
+                revision = cl.revisions.get(pr_status_info.gerrit_sha)
+                if revision:
+                    cl_comment = pr_status_info.to_gerrit_comment(
+                        revision['_number'])
+                else:
+                    cl_comment = pr_status_info.to_gerrit_comment()
+
+                if self.dry_run:
+                    _log.info(
+                        '[dry_run] Would have commented on CL %s\n', change_id)
+                    _log.debug(
+                        'Comments are:\n %s\n', cl_comment)
+                else:
+                    _log.info('Commenting on CL %s\n', change_id)
+                    cl.post_comment(cl_comment)
+            except GerritError as e:
+                _log.error(
+                    'Could not process Gerrit CL %s: %s', change_id, str(e))
+                continue
+
+    def has_latest_taskcluster_status_commented(self, messages, pr_status_info):
+        """Determines if the Taskcluster status has already been commented on the messages of a CL.
+
+        Args:
+            messages: messagese of a CL in JSON Array format, in chronological order.
+            pr_status_info: PRStatusInfo object.
+        """
+        for message in reversed(messages):
+            existing_status = PRStatusInfo.from_gerrit_comment(
+                message['message'])
+            if existing_status:
+                return existing_status.node_id == pr_status_info.node_id
+
+        return False
+
+    def get_failure_taskcluster_status(self, taskcluster_status, pr_number):
+        """Parses Taskcluster status from Taskcluster statuses description field.
+
+        Args:
+            taskcluster_status: array; is of following format:
+                [
+                    {
+                    "url": "https://b",
+                    "avatar_url": "https://a",
+                    "id": 1,
+                    "node_id": "A",
+                    "state": "failure",
+                    "description": "TaskGroup: failure",
+                    "target_url": "https://tools.taskcluster.net/task-group-inspector/#/abc",
+                    "context": "Community-TC (pull_request)",
+                    "created_at": "2019-08-05T22:52:08Z",
+                    "updated_at": "2019-08-05T22:52:08Z"
+                    }
+                ]
+                e.g. https://api.github.com/repos/web-platform-tests/wpt/commits/chromium-export-cl-1407433/status
+            pr_number: The PR number.
+
+        Returns:
+            Taskcluster status dictionary if it has a failure status; None otherwise.
+        """
+        status = None
+        for status_dict in taskcluster_status:
+            if status_dict['context'] == 'Community-TC (pull_request)':
+                status = status_dict
+                break
+
+        if status and status['state'] == 'failure':
+            return status
+
+        if status is None:
+            return None
+
+        assert status['state'] == 'success'
+        _log.debug('Taskcluster status for PR %s is %s', pr_number, status)
+        return None
+
+
+class PRStatusInfo(object):
+    NODE_ID_TAG = 'Taskcluster Node ID: '
+    LINK_TAG = 'Taskcluster Link: '
+    CL_SHA_TAG = 'Gerrit CL SHA: '
+    PATCHSET_TAG = 'Patchset Number: '
+
+    def __init__(self, node_id, link, gerrit_sha=None):
+        self._node_id = node_id
+        self._link = link
+        if gerrit_sha:
+            self._gerrit_sha = gerrit_sha
+        else:
+            self._gerrit_sha = 'Latest'
+
+    @property
+    def node_id(self):
+        return self._node_id
+
+    @property
+    def link(self):
+        return self._link
+
+    @property
+    def gerrit_sha(self):
+        return self._gerrit_sha
+
+    @staticmethod
+    def from_gerrit_comment(comment):
+        tags = [PRStatusInfo.NODE_ID_TAG,
+                PRStatusInfo.LINK_TAG,
+                PRStatusInfo.CL_SHA_TAG]
+        values = ['', '', '']
+
+        for line in comment.splitlines():
+            for index, tag in enumerate(tags):
+                if line.startswith(tag):
+                    values[index] = line[len(tag):]
+
+        for val in values:
+            if not val:
+                return None
+
+        return PRStatusInfo(*values)
+
+    def to_gerrit_comment(self, patchset=None):
+        status_line = ('The exported PR for the current patch failed Taskcluster check(s) '
+                       'on GitHub, which could indict cross-broswer failures on the '
+                       'exportable changes. Please contact ecosystem-infra@ team for '
+                       'more information.')
+        node_id_line = ('\n\n{}{}').format(
+            PRStatusInfo.NODE_ID_TAG, self.node_id)
+        link_line = ('\n{}{}').format(PRStatusInfo.LINK_TAG, self.link)
+        sha_line = ('\n{}{}').format(PRStatusInfo.CL_SHA_TAG, self.gerrit_sha)
+
+        comment = status_line + node_id_line + link_line + sha_line
+        if patchset is not None:
+            comment += ('\n{}{}').format(PRStatusInfo.PATCHSET_TAG, patchset)
+
+        return comment

third_party/blink/tools/blinkpy/w3c/gerrit.py

@@ -58,9 +58,13 @@ class GerritAPI(object):
         }
         return self.host.web.request('POST', url, data=json.dumps(data), headers=headers)
 
-    def query_cl(self, change_id):
-        """Quries a commit information from Gerrit."""
-        path = '/changes/chromium%2Fsrc~master~{}?{}'.format(change_id, QUERY_OPTIONS)
+    def query_cl_comments_and_revisions(self, change_id):
+        """Queries a CL with comments and revisions information."""
+        return self.query_cl(change_id, 'o=MESSAGES&o=ALL_REVISIONS')
+
+    def query_cl(self, change_id, query_options=QUERY_OPTIONS):
+        """Queries a commit information from Gerrit."""
+        path = '/changes/chromium%2Fsrc~master~{}?{}'.format(change_id, query_options)
         try:
             cl_data = self.get(path)
         except NetworkTimeout:
@@ -134,6 +138,14 @@ class GerritCL(object):
     def status(self):
         return self._data['status']
 
+    @property
+    def messages(self):
+        return self._data['messages']
+
+    @property
+    def revisions(self):
+        return self._data['revisions']
+
     def post_comment(self, message):
         """Posts a comment to the CL."""
         path = '/a/changes/{change_id}/revisions/current/review'.format(

third_party/blink/tools/blinkpy/w3c/gerrit_mock.py

@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-from blinkpy.w3c.gerrit import GerritCL, GerritError
+from blinkpy.w3c.gerrit import GerritCL, GerritError, QUERY_OPTIONS
 
 # Some unused arguments may be included to match the real class's API.
 # pylint: disable=unused-argument
@@ -20,7 +20,10 @@ class MockGerritAPI(object):
     def query_exportable_open_cls(self):
         return self.exportable_open_cls
 
-    def query_cl(self, change_id):
+    def query_cl_comments_and_revisions(self, change_id):
+        return self.query_cl(change_id, 'o=MESSAGES&o=ALL_REVISIONS')
+
+    def query_cl(self, change_id, query_options=QUERY_OPTIONS):
         self.cls_queried.append(change_id)
         if self.raise_error:
             raise GerritError("Error from query_cl")

third_party/blink/tools/blinkpy/w3c/test_exporter.py

@@ -19,6 +19,7 @@ from blinkpy.w3c.common import (
 )
 from blinkpy.w3c.gerrit import GerritAPI, GerritCL, GerritError
 from blinkpy.w3c.wpt_github import WPTGitHub, MergeError
+from blinkpy.w3c.export_notifier import ExportNotifier
 
 _log = logging.getLogger(__name__)
 
@@ -84,7 +85,19 @@ class TestExporter(object):
             for error in git_errors:
                 _log.error(error)
 
-        return not (gerrit_error or git_errors)
+        export_error = gerrit_error or git_errors
+        if export_error:
+            return not export_error
+
+        _log.info('Automatic export process has finished successfully.')
+
+        export_notifier_failure = False
+        if options.surface_failures_to_gerrit:
+            _log.info('Starting surfacing cross-browser failures to Gerrit.')
+            export_notifier_failure = ExportNotifier(
+                self.host, self.wpt_github, self.gerrit, self.dry_run).main()
+
+        return not export_notifier_failure
 
     def parse_args(self, argv):
         parser = argparse.ArgumentParser(description=__doc__)
@@ -99,6 +112,10 @@ class TestExporter(object):
             '--credentials-json', required=True,
             help='A JSON file with an object containing zero or more of the '
                  'following keys: GH_USER, GH_TOKEN, GERRIT_USER, GERRIT_TOKEN')
+        parser.add_argument(
+            '--surface-failures-to-gerrit', action='store_true',
+            help='Indicates whether to run the service that surfaces GitHub '
+                 'faliures to Gerrit through comments.')
         return parser.parse_args(argv)
 
     def process_gerrit_cls(self, gerrit_cls):

third_party/blink/tools/blinkpy/w3c/test_exporter_unittest.py

@@ -32,7 +32,8 @@ class TestExporterTest(LoggingTestCase):
     def test_dry_run_stops_before_creating_pr(self):
         test_exporter = TestExporter(self.host)
         test_exporter.wpt_github = MockWPTGitHub(pull_requests=[
-            PullRequest(title='title1', number=1234, body='', state='open', labels=[]),
+            PullRequest(title='title1', number=1234,
+                        body='', state='open', labels=[]),
         ])
         test_exporter.gerrit = MockGerritAPI()
         test_exporter.gerrit.exportable_open_cls = [MockGerritCL(
@@ -52,10 +53,13 @@ class TestExporterTest(LoggingTestCase):
                                                body='fake body', change_id='I001')
         )]
         test_exporter.get_exportable_commits = lambda: ([
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458475}'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458476}'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458475}'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458476}'),
         ], [])
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json', '--dry-run'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json', '--dry-run'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -67,14 +71,19 @@ class TestExporterTest(LoggingTestCase):
 
     def test_creates_pull_request_for_all_exportable_commits(self):
         test_exporter = TestExporter(self.host)
-        test_exporter.wpt_github = MockWPTGitHub(pull_requests=[], create_pr_fail_index=1)
+        test_exporter.wpt_github = MockWPTGitHub(
+            pull_requests=[], create_pr_fail_index=1)
         test_exporter.gerrit = MockGerritAPI()
         test_exporter.get_exportable_commits = lambda: ([
-            MockChromiumCommit(self.host, position='refs/heads/master@{#1}', change_id='I001', subject='subject 1', body='body 1'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#2}', change_id='I002', subject='subject 2', body='body 2'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#3}', change_id='I003', subject='subject 3', body='body 3'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#1}', change_id='I001', subject='subject 1', body='body 1'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#2}', change_id='I002', subject='subject 2', body='body 2'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#3}', change_id='I003', subject='subject 3', body='body 3'),
         ], [])
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -92,8 +101,10 @@ class TestExporterTest(LoggingTestCase):
             'add_label "chromium-export"',
         ])
         self.assertEqual(test_exporter.wpt_github.pull_requests_created, [
-            ('chromium-export-96862edfc1', 'subject 1', 'body 1\n\nChange-Id: I001\n'),
-            ('chromium-export-ce0e78bf18', 'subject 3', 'body 3\n\nChange-Id: I003\n'),
+            ('chromium-export-96862edfc1', 'subject 1',
+             'body 1\n\nChange-Id: I001\n'),
+            ('chromium-export-ce0e78bf18', 'subject 3',
+             'body 3\n\nChange-Id: I003\n'),
         ])
 
     def test_creates_and_merges_pull_requests(self):
@@ -136,13 +147,19 @@ class TestExporterTest(LoggingTestCase):
         ], unsuccessful_merge_index=3)  # Mark the last PR as unmergable.
         test_exporter.gerrit = MockGerritAPI()
         test_exporter.get_exportable_commits = lambda: ([
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458475}', change_id='I0005'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458476}', change_id='I0476'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458477}', change_id='Idead'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458478}', change_id='I0118'),
-            MockChromiumCommit(self.host, position='refs/heads/master@{#458479}', change_id='I0147'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458475}', change_id='I0005'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458476}', change_id='I0476'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458477}', change_id='Idead'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458478}', change_id='I0118'),
+            MockChromiumCommit(
+                self.host, position='refs/heads/master@{#458479}', change_id='I0147'),
         ], [])
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -171,7 +188,8 @@ class TestExporterTest(LoggingTestCase):
             'merge_pr',
         ])
         self.assertEqual(test_exporter.wpt_github.pull_requests_created, [
-            ('chromium-export-52c3178508', 'Fake subject', 'Fake body\n\nChange-Id: I0476\n'),
+            ('chromium-export-52c3178508', 'Fake subject',
+             'Fake body\n\nChange-Id: I0476\n'),
         ])
         self.assertEqual(test_exporter.wpt_github.pull_requests_merged, [3456])
 
@@ -236,7 +254,8 @@ class TestExporterTest(LoggingTestCase):
             api=test_exporter.gerrit,
             chromium_commit=MockChromiumCommit(self.host)
         )]
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -297,7 +316,8 @@ class TestExporterTest(LoggingTestCase):
             MockChromiumCommit(self.host, change_id='decafbad'),
         ], [])
         test_exporter.gerrit = MockGerritAPI()
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -320,7 +340,8 @@ class TestExporterTest(LoggingTestCase):
             MockChromiumCommit(self.host, change_id='decafbad'),
         ], [])
         test_exporter.gerrit = MockGerritAPI()
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [
@@ -359,7 +380,8 @@ class TestExporterTest(LoggingTestCase):
             api=test_exporter.gerrit,
             chromium_commit=MockChromiumCommit(self.host)
         )]
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertTrue(success)
         self.assertEqual(test_exporter.wpt_github.calls, [])
@@ -375,7 +397,8 @@ class TestExporterTest(LoggingTestCase):
         test_exporter.get_exportable_commits = lambda: ([], [])
         test_exporter.gerrit = MockGerritAPI()
         test_exporter.gerrit.query_exportable_open_cls = raise_gerrit_error
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertFalse(success)
         self.assertLog(['INFO: Cloning GitHub web-platform-tests/wpt into /tmp/wpt\n',
@@ -388,9 +411,11 @@ class TestExporterTest(LoggingTestCase):
     def test_run_returns_false_on_patch_failure(self):
         test_exporter = TestExporter(self.host)
         test_exporter.wpt_github = MockWPTGitHub(pull_requests=[])
-        test_exporter.get_exportable_commits = lambda: ([], ['There was an error with the rutabaga.'])
+        test_exporter.get_exportable_commits = lambda: (
+            [], ['There was an error with the rutabaga.'])
         test_exporter.gerrit = MockGerritAPI()
-        success = test_exporter.main(['--credentials-json', '/tmp/credentials.json'])
+        success = test_exporter.main(
+            ['--credentials-json', '/tmp/credentials.json'])
 
         self.assertFalse(success)
         self.assertLog(['INFO: Cloning GitHub web-platform-tests/wpt into /tmp/wpt\n',

third_party/blink/tools/blinkpy/w3c/wpt_github.py

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import base64
+import datetime
 import json
 import logging
 import re
@@ -208,6 +209,48 @@ class WPTGitHub(object):
             state=item['state'],
             labels=labels)
 
+    def recent_failing_chromium_exports(self):
+        """Fetches open PRs with an export label, failing status, and updated
+        within the last month.
+
+        API doc: https://developer.github.com/v3/search/#search-issues-and-pull-requests
+
+        Returns:
+            A list of PullRequest namedtuples.
+        """
+        one_month_ago = datetime.date.today() - datetime.timedelta(days=31)
+        path = (
+            '/search/issues'
+            '?q=repo:{}/{}%20type:pr+is:open%20label:{}%20status:failure%20updated:>{}'
+            '&sort=updated'
+            '&page=1'
+            '&per_page={}'
+        ).format(
+            WPT_GH_ORG,
+            WPT_GH_REPO_NAME,
+            EXPORT_PR_LABEL,
+            one_month_ago.isoformat(),
+            MAX_PER_PAGE
+        )
+
+        failing_prs = []
+        while path is not None:
+            response = self.request(path, method='GET')
+            if response.status_code == 200:
+                if response.data['incomplete_results']:
+                    raise GitHubError('complete results', 'incomplete results',
+                                      'fetch failing open chromium exports', path)
+
+                prs = [self.make_pr_from_item(item) for item in response.data['items']]
+                failing_prs += prs
+            else:
+                raise GitHubError(200, response.status_code,
+                                  'fetch failing open chromium exports', path)
+            path = self.extract_link_next(response.getheader('Link'))
+
+        _log.info('Fetched %d PRs from GitHub.', len(failing_prs))
+        return failing_prs
+
     @memoized
     def all_pull_requests(self):
         """Fetches the most recent (open and closed) PRs with the export label.
@@ -218,7 +261,7 @@ class WPTGitHub(object):
         can't really find *all* of them; we fetch the most recently updated ones
         because we only check whether recent commits have been exported.
 
-        API doc: https://developer.github.com/v3/search/#search-issues
+        API doc: https://developer.github.com/v3/search/#search-issues-and-pull-requests
 
         Returns:
             A list of PullRequest namedtuples.
@@ -258,6 +301,26 @@ class WPTGitHub(object):
         _log.info('Fetched %d PRs from GitHub.', len(all_prs))
         return all_prs
 
+    def get_branch_statuses(self, branch_name):
+        """Gets the status of a PR.
+
+        API doc: https://developer.github.com/v3/repos/statuses/#get-the-combined-status-for-a-specific-ref
+
+        Returns:
+            The list of check statuses of the PR.
+        """
+        path = '/repos/{}/{}/commits/{}/status'.format(
+            WPT_GH_ORG,
+            WPT_GH_REPO_NAME,
+            branch_name
+        )
+        response = self.request(path, method='GET')
+
+        if response.status_code != 200:
+            raise GitHubError(200, response.status_code, 'get the statuses of PR %d' % branch_name)
+
+        return response.data['statuses']
+
     def get_pr_branch(self, pr_number):
         """Gets the remote branch name of a PR.
 

third_party/blink/tools/blinkpy/w3c/wpt_github_mock.py

@@ -23,6 +23,7 @@ class MockWPTGitHub(object):
                 merged. (-1 means none is merged.)
         """
         self.pull_requests = pull_requests
+        self.recent_failing_pull_requests = []
         self.calls = []
         self.pull_requests_created = []
         self.pull_requests_merged = []
@@ -30,11 +31,16 @@ class MockWPTGitHub(object):
         self.create_pr_index = 0
         self.create_pr_fail_index = create_pr_fail_index
         self.merged_index = merged_index
+        self.status = ''
 
     def all_pull_requests(self, limit=30):
         self.calls.append('all_pull_requests')
         return self.pull_requests
 
+    def recent_failing_chromium_exports(self):
+        self.calls.append("recent_failing_chromium_exports")
+        return self.recent_failing_pull_requests
+
     def is_pr_merged(self, number):
         for index, pr in enumerate(self.pull_requests):
             if pr.number == number:
@@ -54,7 +60,8 @@ class MockWPTGitHub(object):
         self.calls.append('create_pr')
 
         if self.create_pr_fail_index != self.create_pr_index:
-            self.pull_requests_created.append((remote_branch_name, desc_title, body))
+            self.pull_requests_created.append(
+                (remote_branch_name, desc_title, body))
 
         self.create_pr_index += 1
         return 5678
@@ -79,6 +86,10 @@ class MockWPTGitHub(object):
         self.calls.append('get_pr_branch')
         return 'fake_branch_PR_%d' % number
 
+    def get_branch_statuses(self, branch_name):
+        self.calls.append('get_branch_statuses')
+        return self.status
+
     def pr_for_chromium_commit(self, commit):
         self.calls.append('pr_for_chromium_commit')
         for pr in self.pull_requests:

third_party/blink/tools/blinkpy/w3c/wpt_github_unittest.py

@@ -50,6 +50,35 @@ class WPTGitHubTest(unittest.TestCase):
     def test_extract_link_next_not_found(self):
         self.assertIsNone(self.wpt_github.extract_link_next(''))
 
+    def test_recent_failing_chromium_exports_single_page(self):
+        self.wpt_github = WPTGitHub(MockHost(), user='rutabaga', token='decafbad', pr_history_window=1)
+        self.wpt_github.host.web.responses = [
+            {'status_code': 200,
+             'headers': {'Link': ''},
+             'body': json.dumps({'incomplete_results': False, 'items': [self.generate_pr_item(1)]})},
+        ]
+
+        self.assertEqual(len(self.wpt_github.recent_failing_chromium_exports()), 1)
+
+    def test_recent_failing_chromium_exports_all_pages(self):
+        self.wpt_github = WPTGitHub(MockHost(), user='rutabaga', token='decafbad', pr_history_window=1)
+        self.wpt_github.host.web.responses = [
+            {'status_code': 200,
+             'headers': {'Link': '<https://api.github.com/resources?page=2>; rel="next"'},
+             'body': json.dumps({'incomplete_results': False, 'items': [self.generate_pr_item(1)]})},
+            {'status_code': 200,
+             'headers': {'Link': ''},
+             'body': json.dumps({'incomplete_results': False, 'items': [self.generate_pr_item(2)]})},
+        ]
+        self.assertEqual(len(self.wpt_github.recent_failing_chromium_exports()), 2)
+
+    def test_recent_failing_chromium_exports_throws_github_error(self):
+        self.wpt_github.host.web.responses = [
+            {'status_code': 204},
+        ]
+        with self.assertRaises(GitHubError):
+            self.wpt_github.recent_failing_chromium_exports()
+
     def test_all_pull_requests_single_page(self):
         self.wpt_github = WPTGitHub(MockHost(), user='rutabaga', token='decafbad', pr_history_window=1)
         self.wpt_github.host.web.responses = [
@@ -122,6 +151,13 @@ class WPTGitHubTest(unittest.TestCase):
         with self.assertRaises(GitHubError):
             self.wpt_github.create_pr('branch', 'title', 'body')
 
+    def test_get_branch_statuses(self):
+        self.wpt_github.host.web.responses = [
+            {'status_code': 200,
+             'body': json.dumps({'statuses': [{'description': 'abc'}]})},
+        ]
+        self.assertEqual(self.wpt_github.get_branch_statuses('1234')[0]['description'], 'abc')
+
     def test_get_pr_branch(self):
         self.wpt_github.host.web.responses = [
             {'status_code': 200,