Specify gpu dimension for network service test in chromium.perf.fyi.json

Bug:717744
Change-Id: I26bc36a78f951b9152e299863d7ff85398b75384

TBR=eyaich@chromium.org

Change-Id: I26bc36a78f951b9152e299863d7ff85398b75384
Reviewed-on: https://chromium-review.googlesource.com/924583Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#537545}

testing/buildbot/chromium.perf.fyi.json

@@ -420,6 +420,7 @@
           "can_use_on_swarming_builders": true,
           "dimension_sets": [
             {
+              "gpu": "10de:1cb3",
               "id": "build113-b4",
               "pool": "Chrome-perf-fyi"
             }