Add commit queue configuration in tools/infra/config

tools/infra/config/cq.cfg

+# See http://luci-config.appspot.com/schemas/projects/refs:cq.cfg for the
+# documentation of this file format.
+version: 1
+cq_name: "dart"
+git_repo_url: "https://dart.googlesource.com/sdk.git"
+rietveld {}
+gerrit {
+}
+verifiers {
+  reviewer_lgtm {
+     committer_list: "dart-team"
+     dry_run_access_list: "dart-team"
+  }
+  gerrit_cq_ability {
+     committer_list: "dart-team"
+     dry_run_access_list: "dart-team"
+  }
+  try_job {
+    buckets {
+      name: "tryserver.client.dart"
+      builders { name: "vm-win-debug-x64-try"}
+      builders { name: "vm-win-release-x64-try"}
+      builders { name: "vm-linux-debug-x64-try"}
+      builders { name: "vm-linux-release-x64-try"}
+      builders { name: "vm-mac-debug-x64-try"}
+      builders { name: "vm-mac-release-x64-try"}
+    }
+  }
+}