Fix https://bugs.chromium.org/p/chromium/issues/detail?id=872922

I'll request a merge into M69 when this is in so we can restart experiments quickly.

Bug: 872922
Change-Id: Icb269a5f6499a5a58a2a51f3348b23e15f20c035
Reviewed-on: https://chromium-review.googlesource.com/1183912
Commit-Queue: Quentin Fiard <qfiard@google.com>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585347}

chrome/browser/google/google_search_domain_mixing_metrics_emitter.cc

@@ -4,6 +4,7 @@
 
 #include "chrome/browser/google/google_search_domain_mixing_metrics_emitter.h"
 
+#include "base/logging.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/history/core/browser/domain_mixing_metrics.h"
 #include "components/history/core/browser/history_backend.h"
@@ -52,7 +53,9 @@ GoogleSearchDomainMixingMetricsEmitter::GoogleSearchDomainMixingMetricsEmitter(
     : prefs_(prefs),
       history_service_(history_service),
       ui_thread_task_runner_(content::BrowserThread::GetTaskRunnerForThread(
-          content::BrowserThread::UI)) {}
+          content::BrowserThread::UI)) {
+  DCHECK(history_service_);
+}
 
 GoogleSearchDomainMixingMetricsEmitter::
     ~GoogleSearchDomainMixingMetricsEmitter() {}

chrome/browser/google/google_search_domain_mixing_metrics_emitter_factory.cc

@@ -43,9 +43,12 @@ KeyedService*
 GoogleSearchDomainMixingMetricsEmitterFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   Profile* profile = Profile::FromBrowserContext(context);
+  auto* history_service = HistoryServiceFactory::GetInstance()->GetForProfile(
+      profile, ServiceAccessType::IMPLICIT_ACCESS);
+  if (history_service == nullptr)
+    return nullptr;
   auto emitter = std::make_unique<GoogleSearchDomainMixingMetricsEmitter>(
-      profile->GetPrefs(), HistoryServiceFactory::GetInstance()->GetForProfile(
-                               profile, ServiceAccessType::IMPLICIT_ACCESS));
+      profile->GetPrefs(), history_service);
   emitter->Start();
   return emitter.release();
 }