WPT Import: Use the "cq_experimental" tag to check for experimental builds

We were previously using the "experimental" field in the JSON returned by
`git-cl try-results`, but that field actually corresponds to whether a
recipe is running in experimental mode. See e.g.

    https://cs.chromium.org/chromium/infra/recipes-py/recipe_modules/runtime/api.py?q=is_experimental&sq=package:chromium&l=27&dr=CSs

What we need is the "cq_experimental" tag that really indicates whether a
trybot is scheduled in an experimental commit queue per

    https://cs.chromium.org/chromium/infra/go/src/infra/libs/bqschema/buildevent/completedbuild.go?type=cs&sq=package:chromium&l=31

This tag is also used by the Buildbucket Gerrit plugin to split bots into
experimental and non-experimental ones.

Bug: 792652, 821445
Change-Id: I267bf033729b6a74382d018cb3da06c64dc7b207
Reviewed-on: https://chromium-review.googlesource.com/964121Reviewed-by: Robert Ma <robertma@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#543385}

third_party/WebKit/Tools/Scripts/webkitpy/common/net/git_cl.py

@@ -196,7 +196,7 @@ class GitCL(object):
             if is_swarming_task and not include_swarming_tasks:
                 continue
             is_cq = 'user_agent:cq' in result.get('tags', [])
-            is_experimental = result.get('experimental')
+            is_experimental = 'cq_experimental:true' in result.get('tags', [])
             if cq_only and not (is_cq and not is_experimental):
                 continue
             build_to_status[self._build(result)] = self._try_job_status(result)

third_party/WebKit/Tools/Scripts/webkitpy/common/net/git_cl_unittest.py

@@ -287,27 +287,61 @@ class GitCLTest(unittest.TestCase):
                 'tags': ['user_agent:cq'],
                 'url': None,
             },
+            {
+                'builder_name': 'cq-b',
+                'experimental': False,
+                'result': None,
+                'status': 'SCHEDULED',
+                'tags': ['cq_experimental:false', 'user_agent:cq'],
+                'url': None,
+            },
+            {
+                'builder_name': 'cq-c',
+                'experimental': True,
+                'result': None,
+                'status': 'SCHEDULED',
+                'tags': ['cq_experimental:false', 'user_agent:cq'],
+                'url': None,
+            },
             {
                 'builder_name': 'cq-a-experimental',
                 'experimental': True,
                 'result': None,
                 'status': 'SCHEDULED',
-                'tags': ['user_agent:cq'],
+                'tags': ['cq_experimental:true', 'user_agent:cq'],
                 'url': None,
             },
             {
-                'builder_name': 'other',
+                'builder_name': 'cq-b-experimental',
+                'experimental': False,
+                'result': None,
+                'status': 'SCHEDULED',
+                'tags': ['cq_experimental:true', 'user_agent:cq'],
+                'url': None,
+            },
+            {
+                'builder_name': 'other-a',
                 'experimental': False,
                 'status': 'SCHEDULED',
                 'result': None,
                 'tags': ['user_agent:git_cl_try'],
                 'url': None,
             },
+            {
+                'builder_name': 'other-b',
+                'experimental': False,
+                'status': 'SCHEDULED',
+                'result': None,
+                'tags': ['is_experimental:false', 'user_agent:git_cl_try'],
+                'url': None,
+            },
         ]
         self.assertEqual(
             git_cl.latest_try_jobs(cq_only=True),
             {
                 Build('cq-a'): TryJobStatus('SCHEDULED'),
+                Build('cq-b'): TryJobStatus('SCHEDULED'),
+                Build('cq-c'): TryJobStatus('SCHEDULED'),
             })
 
     def test_latest_try_jobs(self):