Temporarily remove webkit_layout_tests from mac_chromium_rel_ng.

Tbr: sergeyberezin@chromium.org,bradhall@chromium.org
No-Try: true
Bug: 908551
Change-Id: I5f003793bc94930fa685fff74ae1217e208b0dc6
Reviewed-on: https://chromium-review.googlesource.com/c/1351936Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611103}

testing/buildbot/chromium.mac.json

@@ -3410,30 +3410,6 @@
           ]
         }
       },
-      {
-        "args": [
-          "--num-retries=3"
-        ],
-        "isolate_name": "webkit_layout_tests_exparchive",
-        "merge": {
-          "args": [
-            "--verbose"
-          ],
-          "script": "//third_party/blink/tools/merge_web_test_results.py"
-        },
-        "name": "webkit_layout_tests",
-        "results_handler": "layout tests",
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "gpu": "8086:0a2e",
-              "os": "Mac-10.12.6"
-            }
-          ],
-          "shards": 12
-        }
-      },
       {
         "isolate_name": "webkit_python_tests",
         "name": "webkit_python_tests",

testing/buildbot/test_suite_exceptions.pyl

@@ -1272,6 +1272,8 @@
       'Chromium Mac 10.13',
       # chromium.linux
       'Linux Tests (dbg)(1)(32)', # 32-bit linux is unsupported
+      # chromium.mac
+      'Mac10.12 Tests', # crbug.com/908551
       # chromium.win
       'Win 7 Tests x64 (1)',  # 64-bit win is unsupported by the layout tests.
       'Win10 Tests x64 (dbg)',