buildbot: Enable webkit_layout_tests on swarming.

testing/buildbot/chromium.linux.json

Index: testing/buildbot/chromium.linux.json
diff --git a/testing/buildbot/chromium.linux.json b/testing/buildbot/chromium.linux.json
index e05e1bf098ea0bcbf3152498a3f939f43797e921..5b3f32df7066c86d6f7cb663d3341e2658a29ece 100644
--- a/testing/buildbot/chromium.linux.json
+++ b/testing/buildbot/chromium.linux.json
@@ -3490,6 +3490,35 @@
           "can_use_on_swarming_builders": true,
           "shards": 4
         }
+      },
+      {
+        "isolate_name": "webkit_layout_tests_exparchive",
+        "merge": {
+          "args": [
+            "--verbose",
+            "--results-json-override-with-build-property",
+            "build_number",
+            "buildnumber",
+            "--results-json-override-with-build-property",
+            "builder_name",
+            "buildername",
+            "--results-json-override-with-build-property",
+            "chromium_revision",
+            "got_revision_cp"
+          ],
+          "script": "//third_party/WebKit/Tools/Scripts/merge-layout-test-results"
+        },
+        "name": "webkit_layout_tests",
+        "results_handler": "layout tests",
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "dimension_sets": [
+            {
+              "os": "Ubuntu-14.04"
+            }
+          ],
+          "shards": 6
+        }
       }
     ],
     "scripts": [