[M115][infra] More closely unify variant and mixin behavior.

Variants are logically similar to mixins in their ability to modify a
test suite, with the difference being that a test spec is created for
each variant rather than all being applied to a single test spec. To
ensure more consistent treatment of fields, variants will now use the
mixin codepath to modify a test.

The following differences remain with variants:
* The enabled, identifier and mixins fields specify behavior that is
  specific to variants.
* Skylab details can be specified on a variant under the skylab key.
  When a variant is applied to a test, if the skylab key is present, all
  fields of the value will be lifted to the top-level, except for the
  cros_chrome_version field, which is only used by the cros skylab image
  roller to compare against other data sources.

This CL introduces the following behavior changes:
* The swarming field in a variant is merged in the same way as with a
  mixin, in particular, dimension_sets will be added to the test's
  dimension_sets value instead of merging elements at the same index.
  This didn't result in any changes to generated files, but all variants
  have been updated to use dimensions instead of dimension_sets to
  ensure the same behavior going forward.
* A mixin that specifies the description field (non exist at this
  point), will have the description appended to any existing description
  for the test.

(cherry picked from commit 8d6708c)

Bug: 1456553
Change-Id: I869d8baad76027d811b7c3b96ed35d46509a819b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4703284
Auto-Submit: Garrett Beaty <gbeaty@google.com>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1173053}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4706387
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Cr-Commit-Position: refs/branch-heads/5790@{#1844}
Cr-Branched-From: 1d71a33-refs/heads/main@{#1148114}

infra/config/lib/targets.star

@@ -328,6 +328,7 @@ def _swarming(
 def _mixin(
         *,
         name = None,
+        description = None,
         args = None,
         precommit_args = None,
         android_args = None,
@@ -352,6 +353,9 @@ def _mixin(
 
     Args:
         name: The name of the mixin.
+        description: A description to attach to the test. If specified,
+            it will be appended to any description already present on
+            the test.
         args: Arguments to be passed to the test binary. Will be
             appended to any existing args for the test.
         precommit_args: Arguments to be passed to the test binary when
@@ -394,6 +398,7 @@ def _mixin(
         timeout_sec: The maximum time the test can take to run.
     """
     mixin_values = dict(
+        description = description,
         args = args,
         precommit_args = precommit_args,
         linux_args = linux_args,
@@ -517,6 +522,9 @@ def _generate_mixins_pyl(ctx):
         mixin = n.props.mixin_values
         formatter.open_scope("'{}': {{".format(n.key.id))
 
+        if "description" in mixin:
+            formatter.add_line("'description': '{}',".format(mixin["description"]))
+
         for args_attr in (
             "args",
             "precommit_args",

testing/buildbot/chrome.json

@@ -1552,7 +1552,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "autotest_name": "tast.chrome-from-tls",
         "cros_board": "octopus",
         "cros_img": "octopus-release/R115-15460.0.0",
@@ -1693,7 +1692,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "cros_board": "dedede",
         "cros_img": "dedede-release/R114-15410.0.0",
         "name": "lacros_all_tast_tests DEDEDE_RELEASE_LKGM",
@@ -1709,7 +1707,6 @@
         "variant_id": "DEDEDE_RELEASE_LKGM"
       },
       {
-        "args": [],
         "cros_board": "dedede",
         "cros_img": "dedede-release/R113-15393.12.0",
         "name": "lacros_all_tast_tests DEDEDE_RELEASE_DEV",
@@ -1725,7 +1722,6 @@
         "variant_id": "DEDEDE_RELEASE_DEV"
       },
       {
-        "args": [],
         "cros_board": "dedede",
         "cros_img": "dedede-release/R112-15359.37.0",
         "name": "lacros_all_tast_tests DEDEDE_RELEASE_BETA",
@@ -1741,7 +1737,6 @@
         "variant_id": "DEDEDE_RELEASE_BETA"
       },
       {
-        "args": [],
         "cros_board": "dedede",
         "cros_img": "dedede-release/R111-15329.59.0",
         "name": "lacros_all_tast_tests DEDEDE_RELEASE_STABLE",
@@ -1757,7 +1752,6 @@
         "variant_id": "DEDEDE_RELEASE_STABLE"
       },
       {
-        "args": [],
         "cros_board": "eve",
         "cros_img": "eve-release/R114-15410.0.0",
         "name": "lacros_all_tast_tests EVE_RELEASE_LKGM",
@@ -1773,7 +1767,6 @@
         "variant_id": "EVE_RELEASE_LKGM"
       },
       {
-        "args": [],
         "cros_board": "eve",
         "cros_img": "eve-release/R113-15393.12.0",
         "name": "lacros_all_tast_tests EVE_RELEASE_DEV",
@@ -1789,7 +1782,6 @@
         "variant_id": "EVE_RELEASE_DEV"
       },
       {
-        "args": [],
         "cros_board": "eve",
         "cros_img": "eve-release/R112-15359.37.0",
         "name": "lacros_all_tast_tests EVE_RELEASE_BETA",
@@ -1805,7 +1797,6 @@
         "variant_id": "EVE_RELEASE_BETA"
       },
       {
-        "args": [],
         "cros_board": "eve",
         "cros_img": "eve-release/R111-15329.59.0",
         "name": "lacros_all_tast_tests EVE_RELEASE_STABLE",
@@ -1856,7 +1847,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-release/R114-15410.0.0",
         "name": "lacros_all_tast_tests JACUZZI_RELEASE_LKGM",
@@ -1872,7 +1862,6 @@
         "variant_id": "JACUZZI_RELEASE_LKGM"
       },
       {
-        "args": [],
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-release/R113-15393.12.0",
         "name": "lacros_all_tast_tests JACUZZI_RELEASE_DEV",
@@ -1888,7 +1877,6 @@
         "variant_id": "JACUZZI_RELEASE_DEV"
       },
       {
-        "args": [],
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-release/R112-15359.37.0",
         "name": "lacros_all_tast_tests JACUZZI_RELEASE_BETA",
@@ -1904,7 +1892,6 @@
         "variant_id": "JACUZZI_RELEASE_BETA"
       },
       {
-        "args": [],
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-release/R111-15329.59.0",
         "name": "lacros_all_tast_tests JACUZZI_RELEASE_STABLE",
@@ -1955,7 +1942,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "cros_board": "strongbad",
         "cros_img": "strongbad-release/R114-15410.0.0",
         "name": "lacros_all_tast_tests STRONGBAD_RELEASE_LKGM",

testing/buildbot/chromium.chromiumos.json

@@ -1479,7 +1479,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "eve",
         "cros_img": "eve-public/R114-15410.0.0",
@@ -1499,7 +1498,6 @@
         "variant_id": "EVE_PUBLIC_LKGM"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "eve",
         "cros_img": "eve-public/R113-15393.12.0",
@@ -1519,7 +1517,6 @@
         "variant_id": "EVE_PUBLIC_DEV"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "eve",
         "cros_img": "eve-public/R112-15359.37.0",
@@ -1539,7 +1536,6 @@
         "variant_id": "EVE_PUBLIC_BETA"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "eve",
         "cros_img": "eve-public/R111-15329.59.0",
@@ -1638,7 +1634,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-public/R114-15410.0.0",
@@ -1667,7 +1662,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "kevin",
         "cros_img": "kevin64-public/R114-15410.0.0",

testing/buildbot/chromium.fyi.json

@@ -36806,7 +36806,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "octopus",
         "cros_img": "octopus-public/R114-15410.0.0",
@@ -36823,7 +36822,6 @@
         "variant_id": "OCTOPUS_PUBLIC_LKGM"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "eve",
         "cros_img": "eve-public/R114-15410.0.0",
@@ -36850,7 +36848,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-public/R114-15410.0.0",
@@ -36867,7 +36864,6 @@
         "variant_id": "JACUZZI_PUBLIC_LKGM"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "kevin",
         "cros_img": "kevin64-public/R114-15410.0.0",
@@ -36891,7 +36887,6 @@
     ],
     "skylab_tests": [
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-public/R114-15410.0.0",
@@ -36908,7 +36903,6 @@
         "variant_id": "JACUZZI_PUBLIC_LKGM"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "jacuzzi",
         "cros_img": "jacuzzi-public/R114-15410.0.0",
@@ -36927,7 +36921,6 @@
         "variant_id": "JACUZZI_CQ_PUBLIC_LKGM"
       },
       {
-        "args": [],
         "bucket": "chromiumos-image-archive",
         "cros_board": "kevin",
         "cros_img": "kevin64-public/R114-15410.0.0",