Bug 1696041 - [ci] Remove 'fission-tier' attribute from browsertime-desktop.yml, r=perftest-reviewers,sparky

This change causes a slight change in the taskgraph (see phabricator for diff).
Essentially it changes the optimization for 'browsertime-tp6-firefox' tasks
from 'skip-unless-expanded' to 'skip-unless-backstop'.  This change happened
because the 'apply_raptor_tier_optimization' transform did not take
'fission-tier' into account. Now that 'fission-tier' has merged with 'tier',
these tasks are being modified by this transform. In my view this change is a
desired outcome.

Differential Revision: https://phabricator.services.mozilla.com/D109662

taskcluster/ci/test/browsertime-desktop.yml

@@ -15,7 +15,6 @@ job-defaults:
             default: []
     test-manifest-loader: null  # don't load tests in the taskgraph
     tier: 3
-    fission-tier: 3
     virtualization: hardware
     mozharness:
         script: raptor_script.py
@@ -44,7 +43,6 @@ browsertime-tp6:
     <<: &tp6-defaults
         apps: [firefox, chrome, chromium]
         description: Raptor (browsertime) tp6 page-load tests
-        fission-tier: 2
         fission-run-on-projects:
             by-test-platform:
                 windows7.*: []
@@ -106,9 +104,12 @@ browsertime-tp6:
         - yandex
         - youtube
     tier:
-        by-app:
-            firefox: 2
-            default: 3
+        by-variant:
+            fission: 2
+            default:
+                by-app:
+                    firefox: 2
+                    default: 3
 
 browsertime-tp6-essential:
     <<: *tp6-defaults
@@ -157,17 +158,20 @@ browsertime-benchmark:
     apps: ["firefox"]
     treeherder-symbol: Btime()
     tier:
-        by-app:
-            firefox:
-                by-subtest:
-                    motionmark-animometer: 1
-                    default:
-                        by-test-platform:
-                            windows10-64-ref-hw-2017/opt: 2
-                            windows10-64-ccov.*/.*: 3
-                            linux64-ccov.*/.*: 3
-                            default: 2
-            default: 2
+        by-variant:
+            fission: 3
+            default:
+                by-app:
+                    firefox:
+                        by-subtest:
+                            motionmark-animometer: 1
+                            default:
+                                by-test-platform:
+                                    windows10-64-ref-hw-2017/opt: 2
+                                    windows10-64-ccov.*/.*: 3
+                                    linux64-ccov.*/.*: 3
+                                    default: 2
+                    default: 2
     fission-run-on-projects:
         by-test-platform:
             windows7.*: []
@@ -218,7 +222,6 @@ browsertime-tp6-live:
     <<: *tp6-defaults
     description: Raptor (browsertime) tp6 on live-sites
     fission-run-on-projects: []
-    fission-tier: 3
     mozharness:
         extra-options:
             - --browser-cycles=15
@@ -292,4 +295,8 @@ browsertime-tp6-profiling:
         by-test-platform:
             linux.*shippable[^-qr].*: ['mozilla-central']
             default: []
+    tier:
+        by-variant:
+            fission: 2
+            default: 3
     treeherder-symbol: Btime-Prof(tp6)

taskcluster/taskgraph/transforms/raptor.py

@@ -197,7 +197,9 @@ def split_page_load_by_url(config, tests):
         # `chunk-number` and 'subtest' only exists when the task had a
         # definition for `raptor-subtests`
         chunk_number = test.pop("chunk-number", None)
-        subtest = test.pop("subtest", None)
+        subtest = test.get(
+            "subtest"
+        )  # don't pop as some tasks need this value after splitting variants
         subtest_symbol = test.pop("subtest-symbol", None)
 
         if not chunk_number or not subtest:
@@ -252,7 +254,9 @@ def add_extra_options(config, tests):
             test["attributes"]["run-visual-metrics"] = True
 
         if "app" in test:
-            extra_options.append("--app={}".format(test.pop("app")))
+            extra_options.append(
+                "--app={}".format(test["app"])
+            )  # don't pop as some tasks need this value after splitting variants
 
         if "activity" in test:
             extra_options.append("--activity={}".format(test.pop("activity")))

taskcluster/taskgraph/transforms/tests.py

@@ -411,7 +411,7 @@ test_description_schema = Schema(
         ),
         # the sheriffing tier for this task (default: set based on test platform)
         Optional("tier"): optionally_keyed_by(
-            "test-platform", "variant", Any(int, "default")
+            "test-platform", "variant", "app", "subtest", Any(int, "default")
         ),
         # Same as `tier` except it only applies to Fission tasks. Fission tasks
         # will ignore `tier` and non-Fission tasks will ignore `fission-tier`.
@@ -599,6 +599,12 @@ test_description_schema = Schema(
         },
         # Opt-in to Python 3 support
         Optional("python-3"): bool,
+        # Raptor / browsertime specific keys that need to be here to support
+        # using `by-key` after `by-variant`. Ideally these keys should not exist
+        # in the tests.py schema and instead we'd split variants before the raptor
+        # transforms need them. See bug 1700774.
+        Optional("app"): text_type,
+        Optional("subtest"): text_type,
     }
 )