Create master.tryserver.libyuv bucket

cr-buildbucket.cfg

+# Defines buckets on cr-buildbucket.appspot.com, used by to schedule builds
+# on buildbot. In particular, CQ uses some of these buckets to schedule tryjobs.
+#
+# See http://luci-config.appspot.com/schemas/projects:buildbucket.cfg for
+# schema of this file and documentation.
+#
+# Please keep this list sorted by bucket name.
+
+buckets {
+  name: "master.tryserver.libyuv"

[kjellander_chromium, 2016/01/12 17:43:22]

No bucket needed for master.client.libyuv? I notice WebRTC has one for each
master.

[nodir, 2016/01/12 17:46:37]

what will trigger builds on client bucket?

[kjellander_chromium, 2016/01/12 18:07:56]

Only the Gitiles poller (but that's the same for WebRTC as well).

[nodir, 2016/01/12 18:16:56]

Buildbucket is a transport to buildbot for those running outside master process,
such as git-cl-try, CQ and Rietveld.
GitilesPoller is running inside buildbot process and schedules builds directly
to buildbot. 

[kjellander_chromium, 2016/01/12 20:01:17]

Thanks for explaining. That's how I thought it worked yes. So the additional
buckets for WebRTC are unnecessary as long as only GitilesPoller is used?
Anyway, this should be fine for libyuv then.

+  acls {
+    role: READER
+    group: "all"
+  }
+  acls {
+    role: SCHEDULER
+    group: "project-libyuv-tryjob-access"
+  }
+  acls {
+    role: WRITER
+    identity: "libyuv@chrome-infra-auth.iam.gserviceaccount.com"
+  }
+}