Decouple iOS port from ChromeMetricsServiceClient

This CL changes the iOS port to use IOSChromeMetricsServiceClient rather than
its forked version of ChromeMetricsServiceClient. There is one intended
functional change in that
ChromeMetricsServiceClient::RecordCommandLineMetrics() was not ported to
IOSChromeMetricsServiceClient; see crbug.com/375794 for details.  Other than
that, there should be no functional changes.

BUG=512421, 375794

Review URL: https://codereview.chromium.org/1470963002

Cr-Commit-Position: refs/heads/master@{#361103}

ios/chrome/browser/prefs/browser_prefs.mm

@@ -29,6 +29,7 @@
 #include "ios/chrome/browser/first_run/first_run.h"
 #import "ios/chrome/browser/geolocation/omnibox_geolocation_local_state.h"
 #import "ios/chrome/browser/memory/memory_debugger_manager.h"
+#import "ios/chrome/browser/metrics/ios_chrome_metrics_service_client.h"
 #include "ios/chrome/browser/net/http_server_properties_manager_factory.h"
 #include "ios/chrome/browser/pref_names.h"
 #include "ios/chrome/browser/signin/signin_manager_factory.h"
@@ -50,6 +51,7 @@ void RegisterLocalStatePrefs(PrefRegistrySimple* registry) {
   BrowserStateInfoCache::RegisterPrefs(registry);
   gcm::GCMChannelStatusSyncer::RegisterPrefs(registry);
   ios::SigninManagerFactory::RegisterPrefs(registry);
+  IOSChromeMetricsServiceClient::RegisterPrefs(registry);
   network_time::NetworkTimeTracker::RegisterPrefs(registry);
   PrefProxyConfigTrackerImpl::RegisterPrefs(registry);
   rappor::RapporService::RegisterPrefs(registry);