Pass MetricsServiceClient into MetricsService, and create a simple stubbed TestMetricsServiceClient…

chrome/browser/metrics/metrics_service.cc

 // Copyright (c) 2012 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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 440 matching lines @@
   registry->RegisterInt64Pref(prefs::kUninstallLaunchCount, 0);
   registry->RegisterInt64Pref(prefs::kUninstallMetricsUptimeSec, 0);
   registry->RegisterInt64Pref(prefs::kUninstallLastLaunchTimeSec, 0);
   registry->RegisterInt64Pref(prefs::kUninstallLastObservedRunTimeSec, 0);
 
 #if defined(OS_ANDROID)
   RegisterPrefsAndroid(registry);
 #endif  // defined(OS_ANDROID)
 }
 
-MetricsService::MetricsService(metrics::MetricsStateManager* state_manager)
+MetricsService::MetricsService(metrics::MetricsStateManager* state_manager,
+                               metrics::MetricsServiceClient* client)
     : MetricsServiceBase(g_browser_process->local_state(),
                          kUploadLogAvoidRetransmitSize),
       state_manager_(state_manager),
+      client_(client),
       recording_active_(false),
       reporting_active_(false),
       test_mode_active_(false),
       state_(INITIALIZED),
       has_initial_stability_log_(false),
       idle_since_last_transmission_(false),
       session_id_(-1),
       next_window_id_(0),
       self_ptr_factory_(this),
       state_saver_factory_(this),
       waiting_for_asynchronous_reporting_step_(false),
       num_async_histogram_fetches_in_progress_(0) {
   DCHECK(IsSingleThreaded());
   DCHECK(state_manager_);
+  DCHECK(client_);
 
   BrowserChildProcessObserver::Add(this);
 }
 
 MetricsService::~MetricsService() {
   DisableRecording();
 
   BrowserChildProcessObserver::Remove(this);
 }
 
@@ skipping 1503 matching lines @@
   if (metrics_service)
     metrics_service->AddObserver(observer);
 }
 
 void MetricsServiceHelper::RemoveMetricsServiceObserver(
     MetricsServiceObserver* observer) {
   MetricsService* metrics_service = g_browser_process->metrics_service();
   if (metrics_service)
     metrics_service->RemoveObserver(observer);
 }