Get rid of "default:" clause.

chrome/browser/chromeos/arc/arc_auth_service.cc

Index: chrome/browser/chromeos/arc/arc_auth_service.cc
diff --git a/chrome/browser/chromeos/arc/arc_auth_service.cc b/chrome/browser/chromeos/arc/arc_auth_service.cc
index a342fc0878629bbb990c39a4211cd71a78bb7bc8..dcfe9a697afdb9e21871de35c34f38b1a1f8e417 100644
--- a/chrome/browser/chromeos/arc/arc_auth_service.cc
+++ b/chrome/browser/chromeos/arc/arc_auth_service.cc
@@ -1146,10 +1146,12 @@ std::ostream& operator<<(std::ostream& os, const ArcAuthService::State& state) {
       return os << "FETCHING_CODE";
     case ArcAuthService::State::ACTIVE:
       return os << "ACTIVE";
-    default:
-      NOTREACHED();
-      return os;
   }
+
+  // Some compiler reports an error even if all values of an enum-class are
+  // covered indivisually in a switch statement.
+  NOTREACHED();
+  return os;
 }
 
 }  // namespace arc