Register LUCI "WebKit Mac Builder (dbg)" builder in cr-buildbucket.

R=nodir@chromium.org

Bug: 790322
Change-Id: Ibe0e7df0763c92f8ea16f7ca70afe45fa2a04e6b
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/936241Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539027}

infra/config/global/cr-buildbucket.cfg

@@ -161,6 +161,13 @@ builder_mixins {
   }
 }
 
+builder_mixins {
+  name: "webkit-ci"
+  recipe {
+    properties: "mastername:chromium.webkit"
+  }
+}
+
 builder_mixins {
   name: "win"
   dimensions: "os:Windows"
@@ -299,6 +306,14 @@ buckets {
       dimensions: "cores:8"
     }
 
+    builders {
+      name: "WebKit Mac Builder (dbg)"
+      mixins: "webkit-ci"
+      dimensions: "os:Mac-10.13"
+      dimensions: "cpu:x86-64"
+      dimensions: "cores:8"
+    }
+
     # Win bots.
     builders {
       name: "Win Builder (dbg)"