infra: Migrate builders to Goma RBE (Week 2.5)

CI Builders migrated:
- Linux Builder
- GPU Linux Builder

Corresponding CQ builders migrated:
- linux-rel
- linux-dcheck-off-rel
- linux_chromium_compile_rel_ng

Bug: 950413
Change-Id: I5672b95ac72e46d9218c0b50c2ae361a502ffbcb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648538Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667285}

infra/config/cr-buildbucket.cfg

@@ -1452,7 +1452,7 @@ buckets {
 
     builders {
       name: "Linux Builder"
-      mixins: "linux-ci"
+      mixins: "linux-ci-goma-rbe-prod"
       mixins: "linux-xenial"
       dimensions: "cores:32"
     }
@@ -1571,6 +1571,7 @@ buckets {
     builders {
       name: "GPU Linux Builder"
       mixins: "linux-gpu-ci"
+      mixins: "goma-rbe-prod"
     }
 
     builders {
@@ -3802,7 +3803,11 @@ buckets {
       name: "linux-blink-heap-concurrent-marking-tsan-rel"
     }
     builders { mixins: "linux-try" name: "linux-blink-heap-verification-try" }
-    builders { mixins: "linux-try" name: "linux-dcheck-off-rel" }
+    builders {
+      mixins: "linux-try"
+      mixins: "goma-rbe-prod"
+      name: "linux-dcheck-off-rel"
+    }
     builders {
       mixins: "linux-try"
       mixins: "goma-j150"
@@ -3875,6 +3880,7 @@ buckets {
     }
     builders {
       mixins: "linux-try"
+      mixins: "goma-rbe-prod"
       name: "linux_chromium_compile_rel_ng"
     }
     builders {
@@ -3903,7 +3909,7 @@ buckets {
     builders {
       mixins: "linux-try"
       mixins: "linux-xenial"
-      mixins: "goma-j150"
+      mixins: "goma-rbe-prod-j150"
       mixins: "builderless"
       name: "linux-rel"
     }

infra/config/luci-milo.cfg

@@ -2985,6 +2985,15 @@ consoles {
     category: "week2d|mac"
     short_name: "jumbo"
   }
+  builders {
+    name: "buildbucket/luci.chromium.ci/Linux Builder"
+    category: "week2.5|linux"
+  }
+  builders {
+    name: "buildbucket/luci.chromium.ci/GPU Linux Builder"
+    category: "week2.5|linux"
+    short_name: "gpu"
+  }
 }
 
 consoles {