[iOS] Fixing crash in privacy settings

When unified consent is enabled, Privacy settings should not observe
metric reporting preferences. The metric reporting settings has been
moved Google Services settings.

Bug: 998500
Change-Id: I8e3cc2f91a88d373bf9e28ed3eacbe3d1b78d25f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1776048Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691653}

ios/chrome/browser/ui/settings/privacy_table_view_controller.mm

@@ -135,6 +135,7 @@ GURL kGoogleServicesSettingsURL("settings://open_google_services");
     // screen.
     _prefObserverBridge->ObserveChangesForPreference(
         prefs::kIosHandoffToOtherDevices, &_prefChangeRegistrar);
+    if (!unified_consent::IsUnifiedConsentFeatureEnabled()) {
       _prefObserverBridge->ObserveChangesForPreference(
           metrics::prefs::kMetricsReportingEnabled,
           &_prefChangeRegistrarApplicationContext);
@@ -142,6 +143,7 @@ GURL kGoogleServicesSettingsURL("settings://open_google_services");
           prefs::kMetricsReportingWifiOnly,
           &_prefChangeRegistrarApplicationContext);
     }
+  }
   return self;
 }
 
@@ -507,6 +509,7 @@ GURL kGoogleServicesSettingsURL("settings://open_google_services");
 
   if (preferenceName == metrics::prefs::kMetricsReportingEnabled ||
       preferenceName == prefs::kMetricsReportingWifiOnly) {
+    DCHECK(!unified_consent::IsUnifiedConsentFeatureEnabled());
     if (base::FeatureList::IsEnabled(kUmaCellular)) {
       bool isOn = GetApplicationContext()->GetLocalState()->GetBoolean(
           metrics::prefs::kMetricsReportingEnabled);