Move more metrics classes to metrics namespace.

base/threading/thread_restrictions.h

Index: base/threading/thread_restrictions.h
diff --git a/base/threading/thread_restrictions.h b/base/threading/thread_restrictions.h
index 2288049475343341985cd7d846347afc505d4fff..3c8612d472c4fa558edef5c32c3eb52b6724c131 100644
--- a/base/threading/thread_restrictions.h
+++ b/base/threading/thread_restrictions.h
@@ -18,7 +18,6 @@
 class AcceleratedPresenter;
 class BrowserProcessImpl;
 class HistogramSynchronizer;
-class MetricsService;
 class NativeBackendKWallet;
 class ScopedAllowWaitForLegacyWebViewApi;
 class TestingAutomationProvider;
@@ -61,6 +60,9 @@ class InFlightIO;
 namespace media {
 class AudioOutputController;
 }
+namespace metrics {
+class MetricsService;
+}
 namespace mojo {
 namespace common {
 class WatcherThreadManager;
@@ -223,7 +225,7 @@ class BASE_EXPORT ThreadRestrictions {
   friend class net::internal::AddressTrackerLinux;  // http://crbug.com/125097
   friend class ::AcceleratedPresenter;            // http://crbug.com/125391
   friend class ::BrowserProcessImpl;              // http://crbug.com/125207
-  friend class ::MetricsService;                  // http://crbug.com/124954
+  friend class metrics::MetricsService;           // http://crbug.com/124954
   friend class ::NativeBackendKWallet;            // http://crbug.com/125331
   // END USAGE THAT NEEDS TO BE FIXED.