Move disk_usage_tast_test CrOS VM test into pool=chromium.tests.

url_unittests was moved over earlier, but it gets deduped almost 80% of
the time, so doesn't provide much signal.

disk_usage_tast_test isn't marked idempotent, so will never be deduped.
It also runs pretty quickly (~2 min), so shouldn't use up an excessive
amount of test pool resources.

Bug: 1132206
Change-Id: Ibcd6b199cf635280bb5b99e890c9080c3293ed6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2458769Reviewed-by: Haiyang Pan <hypan@google.com>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814862}

testing/buildbot/chromium.chromiumos.json

@@ -212,12 +212,26 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
+              "cpu": "x86",
               "kvm": "1",
               "os": "Ubuntu-16.04",
-              "pool": "chromium.tests.cros.vm"
+              "pool": "chromium.tests"
             }
           ],
           "idempotent": false,
+          "named_caches": [
+            {
+              "name": "cros_vm",
+              "path": "magic_cros_vm_cache"
+            }
+          ],
+          "optional_dimensions": {
+            "60": [
+              {
+                "caches": "cros_vm"
+              }
+            ]
+          },
           "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com"
         },
         "test": "disk_usage_tast_test",

testing/buildbot/test_suite_exceptions.pyl

@@ -1146,6 +1146,33 @@
     ],
   },
   'disk_usage_tast_test': {
+    'modifications': {
+      # TODO(crbug.com/1132206): Apply this to all of the bot's tests if the
+      # cache affinity works.
+      'chromeos-amd64-generic-rel': {
+        'swarming': {
+          'dimension_sets': [
+            {
+              'cpu': 'x86',
+              'pool': 'chromium.tests',
+            }
+          ],
+          'optional_dimensions': {
+            '60': [
+              {
+                'caches': 'cros_vm',
+              }
+            ],
+          },
+          'named_caches': [
+            {
+              'name': 'cros_vm',
+              'path': 'magic_cros_vm_cache',
+            },
+          ],
+        },
+      },
+    },
     # TODO(crbug.com/1077659): Add the test back after it's fixed.
     'remove_from': [
       'chromeos-kevin-rel',