Add support for single sample metrics.

components/test/BUILD.gn

 # Copyright 2016 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.
 
 source_set("test_support") {
   testonly = true
 
   sources = [
     "components_test_suite.cc",
     "components_test_suite.h",
   ]
 
   deps = [
     "//components/content_settings/core/common",
     "//components/gcm_driver:gcm_driver",
     "//components/signin/core/browser",
+    "//mojo/edk/system",
     "//net",
     "//testing/gtest",
     "//ui/base",
     "//ui/resources:ui_test_pak",
   ]
 
   public_deps = [
     "//base/test:test_support",
   ]
 
   if (!is_ios) {
     deps += [
       "//components/invalidation/impl",
       "//components/policy/core/browser",
       "//components/safe_json",
       "//ui/gl:test_support",
     ]
 
     public_deps += [ "//content/test:test_support" ]
   }
 }