[Unity] Use pref to get UMA state for unified consent

This CL changes ChromeUnifiedConsentClient to use
kMetricsReportingEnabled pref to check whether UMA reporting is enabled,
as IsMetricsAndCrashReportingEnabled always returns false on
non-official builds, forcing unified consent to be off.

Bug: 814728
Change-Id: Ie39ca8d23cdc1fbb757a5ec74c719092c758a1d6
Reviewed-on: https://chromium-review.googlesource.com/1183679Reviewed-by: Thomas Tangl <tangltom@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585053}

chrome/browser/unified_consent/chrome_unified_consent_service_client.cc

@@ -48,8 +48,10 @@ ChromeUnifiedConsentServiceClient::GetServiceState(Service service) {
       enabled = pref_service_->GetBoolean(prefs::kAlternateErrorPagesEnabled);
       break;
     case Service::kMetricsReporting:
-      enabled =
-          ChromeMetricsServiceAccessor::IsMetricsAndCrashReportingEnabled();
+      // Uploads are disabled for non-official builds, but UnifiedConsentService
+      // only cares whether the user has manually disabled metrics reporting.
+      enabled = g_browser_process->local_state()->GetBoolean(
+          metrics::prefs::kMetricsReportingEnabled);
       break;
     case Service::kNetworkPrediction:
       enabled = pref_service_->GetInteger(prefs::kNetworkPredictionOptions) ==