Add Goma Latest builders for iOS and ChromeOS to buildbucket.

We seem not add iOS and ChromeOS builders to cr-buildbucket.cfg.
I suppose that might be the reason why we did not see any updates for
the builders in milo.  Let me try to add them.

Bug: 874754
Change-Id: I72969147d3199cffad4c543cd88f7693bacd26c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1501632
Auto-Submit: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Commit-Queue: Fumitoshi Ukai <ukai@chromium.org>
Reviewed-by: Fumitoshi Ukai <ukai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637562}

infra/config/cr-buildbucket.cfg

@@ -2864,6 +2864,20 @@ buckets {
       dimensions: "os:Ubuntu-14.04"
       mixins: "fyi-ci"
     }
+    builders {
+      name: "chromeos-amd64-generic-rel-goma-latest"
+      dimensions: "os:Ubuntu-14.04"
+      mixins: "fyi-ci"
+    }
+    builders {
+      name: "ios-device-goma-canary-latest"
+      dimensions: "os:Mac-10.13"
+      dimensions: "cores:4"
+      mixins: "fyi-ci"
+      recipe {
+        name: "ios/unified_builder_tester"
+      }
+    }
   }
 }