[test] Add swarming dimensions for v8-side test specs

NOTRY=true

Bug: chromium:830557
Change-Id: Iccd9a6e586d388c55382dd0fbb51d2b62922b8c5
Reviewed-on: https://chromium-review.googlesource.com/1041689
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52938}

infra/testing/PRESUBMIT.py

@@ -21,7 +21,7 @@ SUPPORTED_BUILDER_SPEC_KEYS = [
 # This is not an exhaustive list. It only reflects what we currently use. If
 # there's need to specify a different dimension, just add it here.
 SUPPORTED_SWARMING_DIMENSIONS = [
-  'cores'
+  'cores',
   'cpu',
   'os',
 ]

infra/testing/tryserver.v8.pyl

@@ -16,6 +16,9 @@
     ],
   },
   'v8_linux_rel_ng_triggered': {
+    'swarming_dimensions' : {
+      'cpu': 'x86-64-avx2',
+    },
     'tests': [
       {'name': 'benchmarks'},
       {'name': 'benchmarks', 'variant': 'extra'},