luci: add buildbucket configuration for android_cronet_tester.

Should allow luci-migration to experiment on this despite the rename.
Also removes a no-longer-necessary similar configuration for
android-marshmallow-arm64-rel's old name.

Bug: 731988
Change-Id: Ie806043618101a943f9e8fcf6b24fd85f5fc187b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1580759
Auto-Submit: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653589}

infra/config/cr-buildbucket.cfg

@@ -3377,6 +3377,15 @@ buckets {
     builders { mixins: "android-angle-try" name: "android_angle_vk32_rel_ng" }
     builders { mixins: "android-angle-try" name: "android_angle_vk64_deqp_rel_ng" }
     builders { mixins: "android-angle-try" name: "android_angle_vk64_rel_ng" }
+    builders {
+      mixins: "android-try"
+      mixins: "builderless"
+      name: "android_cronet_tester"
+      dimensions: "os:Ubuntu-14.04"
+      recipe {
+        properties: "buildername:android-cronet-arm-dbg"
+      }
+    }
     builders {
       mixins: "android-try"
       mixins: "builderless"
@@ -3402,20 +3411,6 @@ buckets {
       name: "android-oreo-arm64-cts-networkservice-dbg"
       dimensions: "os:Ubuntu-14.04"
     }
-    # TODO(jbudorick): Remove this after fully migrating ANSR.
-    builders {
-      mixins: "android-try"
-      mixins: "goma-j150"
-      name: "android_n5x_swarming_rel"
-      auto_builder_dimension: NO
-      dimensions: "builder:android-marshmallow-arm64-rel"
-      dimensions: "os:Ubuntu-14.04"
-      # TODO(hinoka): Make this 16 core after crbug.com/875708
-      dimensions: "cores:"
-      recipe {
-        properties: "buildername:android-marshmallow-arm64-rel"
-      }
-    }
     builders {
       mixins: "android-try"
       mixins: "goma-j300"