Move chromium.dev's tests to a pool with templates.

Needs crrev.com/c/2070324 landed & deployed to staging before this can
land.

Bug: 812428
Change-Id: I06d240b78dfcb8d7b5e735a5c67498c55041c9c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057783Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744772}

testing/buildbot/mixins.pyl

@@ -164,6 +164,15 @@
       },
     },
   },
+  # TODO(crbug.com/812428): Remove this mixin after all test pools have migrated
+  # to using templates.
+  'chromium-template-pool': {
+    'swarming': {
+      'dimensions': {
+        'pool': 'chromium.tests.template',
+      },
+    },
+  },
   'code-coverage': {
     'isolate_coverage_data': True,
   },

testing/buildbot/waterfalls.pyl

@@ -1348,6 +1348,7 @@
     'machines': {
       'android-kitkat-arm-rel-swarming': {
         'mixins': [
+          'chromium-template-pool',
           'kitkat',
           'hammerhead',
         ],
@@ -1360,6 +1361,9 @@
         'os_type': 'android',
       },
       'android-marshmallow-arm64-rel-swarming': {
+        'mixins': [
+          'chromium-template-pool',
+        ],
         'test_suites': {
            'gtest_tests': 'chromium_swarm_android_gtests',
         },
@@ -1378,17 +1382,24 @@
       'linux-rel-swarming': {
         'mixins': [
           'linux-xenial',
+          'chromium-template-pool',
         ],
         'test_suites': {
            'gtest_tests': 'chromium_swarm_linux_gtests',
         },
       },
       'mac-rel-swarming': {
+        'mixins': [
+          'chromium-template-pool',
+        ],
         'test_suites': {
            'gtest_tests': 'chromium_swarm_desktop_gtests',
         },
       },
       'win-rel-swarming': {
+        'mixins': [
+          'chromium-template-pool',
+        ],
         'test_suites': {
            'gtest_tests': 'chromium_swarm_desktop_gtests',
         },