Reenable webkit_layout_tests on Mac10.12 Tests.

Note that this does not affect mac_chromium_rel_ng.

Bug: 908929
Change-Id: I4834ae78bb0e037a2def2fd73762b5a90c0ef949
Reviewed-on: https://chromium-review.googlesource.com/c/1354131Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612001}

testing/buildbot/chromium.mac.json

@@ -3410,6 +3410,30 @@
           ]
         }
       },
+      {
+        "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

@@ -1289,7 +1289,6 @@
       # chromium.linux
       'Linux Tests (dbg)(1)(32)', # 32-bit linux is unsupported
       # chromium.mac
-      'Mac10.12 Tests', # crbug.com/908551
       'Mac10.13 Tests', # crbug.com/908551
       # chromium.win
       'Win 7 Tests x64 (1)',  # 64-bit win is unsupported by the layout tests.