Increase -j 80 -> 150 for mac_chromium_rel_ng builder

Let me improve compile step time for mac_chromium_rel_ng builder.

This is mainly to improve some slow compile step on the builder.
But also aims to mitigate total CQ time heavily affected by very slow webkit_layout_tests like below builds.

8253s (total) and 2431s (compile): https://ci.chromium.org/b/8942705844272728000
7389s (total) and 3601s (compile): https://ci.chromium.org/b/8942775029613500944
7321s (total) and 2489s (compile): https://ci.chromium.org/b/8942701297855457248
7105s (total) and 3355s (compile): https://ci.chromium.org/b/8942762808006546480
6681s (total) and 3702s (compile): https://ci.chromium.org/b/8942774232656410784

Bug: 851355, 804251
Change-Id: Id81e97b9733e87b4445414e5e096f412119f8405
Reviewed-on: https://chromium-review.googlesource.com/1114397Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570355}

infra/config/global/cr-buildbucket.cfg

@@ -2592,7 +2592,11 @@ buckets {
     builders { mixins: "mac-try" name: "mac_chromium_compile_rel_ng" }
     builders { mixins: "mac-try" name: "mac_chromium_dbg_ng" dimensions:"os:Mac-10.12"}
     builders { mixins: "mac-try" mixins: "gn_upload" name: "mac_chromium_gn_upload" }
-    builders { mixins: "mac-try" name: "mac_chromium_rel_ng" }
+    builders {
+      mixins: "mac-try"
+      mixins: "goma-j150"
+      name: "mac_chromium_rel_ng"
+    }
     builders { mixins: "mac-try" name: "mac_chromium_variable" }
     builders { mixins: "mac-try" name: "mac_chromium_variable_10.10" }
     builders { mixins: "mac-try" name: "mac_chromium_variable_10.10_layout" }