Add trace event in HostContentSettingsMap constructor

Helps to show the impact of settings parsing in startup.

BUG=890129

Change-Id: Ia92ebd734600a9114b7cffaf1296d7ada2d1c4f5
Reviewed-on: https://chromium-review.googlesource.com/c/1260142Reviewed-by: Balazs Engedy <engedy@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Commit-Queue: Siddhartha S <ssid@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599713}

components/content_settings/core/browser/host_content_settings_map.cc

@@ -18,6 +18,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/clock.h"
+#include "base/trace_event/trace_event.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "components/content_settings/core/browser/content_settings_default_provider.h"
@@ -210,6 +211,7 @@ HostContentSettingsMap::HostContentSettingsMap(
       is_incognito_(is_incognito_profile || is_guest_profile),
       store_last_modified_(store_last_modified),
       weak_ptr_factory_(this) {
+  TRACE_EVENT0("startup", "HostContentSettingsMap::HostContentSettingsMap");
   DCHECK(!(is_incognito_profile && is_guest_profile));
 
   content_settings::PolicyProvider* policy_provider =