Run layout tests under swarming on 10.11 (dbg), retina builders.

The "WebKit Mac 10.11 (dbg)" and "WebKit Mac Retina" builders
are still running the layout tests locally. This CL should switch
them to run under swarming (and switch the corresponding trybots).

R=qyearsley@chromium.org
BUG=524758


Change-Id: I06297fc45dce187b02cef83d3df80d2638d51fbb
Reviewed-on: https://chromium-review.googlesource.com/747843
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513165}

testing/buildbot/chromium.webkit.json

@@ -409,6 +409,29 @@
         "test": "wtf_unittests"
       }
     ],
+    "isolated_scripts": [
+      {
+        "isolate_name": "webkit_layout_tests_exparchive",
+        "merge": {
+          "args": [
+            "--verbose"
+          ],
+          "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": [
+            {
+              "gpu": "none",
+              "os": "Mac-10.11.6"
+            }
+          ],
+          "shards": 4
+        }
+      }
+    ],
     "scripts": [
       {
         "name": "webkit_lint",
@@ -435,6 +458,31 @@
         "test": "wtf_unittests"
       }
     ],
+    "isolated_scripts": [
+      {
+        "isolate_name": "webkit_layout_tests_exparchive",
+        "merge": {
+          "args": [
+            "--verbose"
+          ],
+          "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": [
+            {
+              "gpu": "1002:6821",
+              "hidpi": "1",
+              "os": "Mac-10.12.6",
+              "pool": "Chrome-GPU"
+            }
+          ],
+          "shards": 4
+        }
+      }
+    ],
     "scripts": [
       {
         "name": "webkit_lint",