tools/battor_agent: Adds battor_agent_unittests to waterfall

BUG=571458

Review URL: https://codereview.chromium.org/1645103002

Cr-Commit-Position: refs/heads/master@{#372214}

diff --git a/BUILD.gn b/BUILD.gn
index d644a5d..c1bc7cb 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -149,6 +149,7 @@
       "//third_party/codesighs",
       "//third_party/pdfium/samples:pdfium_test",
       "//tools/battor_agent",
+      "//tools/battor_agent:battor_agent_unittests",
       "//tools/gn",
       "//tools/gn:gn_unittests",
       "//tools/perf/clear_system_cache",