Add UKM initial_url and session_id fields.

components/ukm/BUILD.gn

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 # The Url-Keyed Metrics (UKM) service is responsible for gathering and
 # uploading reports that contain fine grained performance metrics including
 # URLs for top-level navigations.
 static_library("ukm") {
@@ skipping 67 matching lines @@
   deps = [
     ":observers",
     ":test_support",
     ":ukm",
     "//base",
     "//base/test:test_support",
     "//components/metrics",
     "//components/metrics:test_support",
     "//components/prefs:test_support",
     "//components/sync:test_support_driver",
+    "//components/variations",
     "//net:test_support",
     "//testing/gtest",
     "//third_party/zlib:compression_utils",
     "//url",
   ]
 }
 
 # Convenience testing target
 test("ukm_unittests") {
   deps = [
     ":unit_tests",
     "//base",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
   ]
 }