Fix L10nUtilTest flakiness by shutting down StatisticsProvider

Bug: 939160
Change-Id: I9371553975c56bb19450aed1ac12296708c0e412
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1507233Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638614}

chrome/browser/ui/webui/chromeos/login/l10n_util_unittest.cc

@@ -75,6 +75,7 @@ L10nUtilTest::L10nUtilTest()
 }
 
 L10nUtilTest::~L10nUtilTest() {
+  chromeos::system::StatisticsProvider::GetInstance()->Shutdown();
   chromeos::input_method::Shutdown();
 }