Move the thread hop for UMA user actions from content:: to base::.

components/metrics/BUILD.gn

 # Copyright 2014 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.
 
 declare_args() {
   # Overrides os name in uma metrics log to "Blimp".
   metrics_use_blimp = false
 }
 
 # GYP version: components/metrics.gypi:metrics
@@ skipping 240 matching lines @@
       ":profiler",
     ]
     deps = [
       "//base",
     ]
   }
 }
 
 # GYP version: components/metrics.gypi:metrics_test_support
 source_set("test_support") {
+  testonly = true
   sources = [
     "test_metrics_provider.cc",
     "test_metrics_provider.h",
     "test_metrics_service_client.cc",
     "test_metrics_service_client.h",
   ]
 
   public_deps = [
     ":metrics",
   ]
@@ skipping 89 matching lines @@
   # These are only used by the blimp team, which has entirely migrated to gn,
   # so this logic is not replicated in the gyp file.
   if (metrics_use_blimp) {
     defines = [
       "OVERRIDE_OS_NAME_TO_BLIMP",
       "ENABLE_REPORTING_BLIMP",
     ]
   }
 }
 # TODO(GYP): metrics_chromeos