Add trace event in BrowserPolicyConnector

Helps to measure why BrowserPolicyConnector::IsNonEnterpriseUser()
sometimes takes too long to run on main thread.

BUG=891476

Change-Id: I5dd76dfb22a3334dc1015cf6d6c1f23c7e6f2da0
Reviewed-on: https://chromium-review.googlesource.com/c/1280550Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Commit-Queue: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599726}

components/policy/core/browser/browser_policy_connector.cc

@@ -17,6 +17,7 @@
 #include "base/strings/string16.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/trace_event/trace_event.h"
 #include "components/policy/core/common/cloud/cloud_policy_refresh_scheduler.h"
 #include "components/policy/core/common/cloud/device_management_service.h"
 #include "components/policy/core/common/configuration_policy_provider.h"
@@ -133,6 +134,7 @@ void BrowserPolicyConnector::ScheduleServiceInitialization(
 
 // static
 bool BrowserPolicyConnector::IsNonEnterpriseUser(const std::string& username) {
+  TRACE_EVENT0("browser", "BrowserPolicyConnector::IsNonEnterpriseUser");
   if (username.empty() || username.find('@') == std::string::npos) {
     // An empty username means incognito user in case of ChromiumOS and
     // no logged-in user in case of Chromium (SigninService). Many tests use