Trace the content_settings::PrefProvider constructor.

Add a TRACE_EVENT to track how long it takes to initialize
content_settings::PrefProvider, and record the number of exceptions parsed.

Bug: 890129
Change-Id: Ic70783bc9c69f4ce0fdb84e5406701b59bbcbd10
Reviewed-on: https://chromium-review.googlesource.com/c/1326150Reviewed-by: oysteine <oysteine@chromium.org>
Reviewed-by: Martin Šrámek <msramek@chromium.org>
Reviewed-by: ssid <ssid@chromium.org>
Commit-Queue: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606976}

chrome/common/trace_event_args_whitelist.cc

@@ -36,6 +36,7 @@ const WhitelistEntry kEventArgsWhitelist[] = {
     {"ipc", "SyncChannel::Send", nullptr},
     {"latencyInfo", "*", kInputLatencyAllowedArgs},
     {"shutdown", "*", nullptr},
+    {"startup", "PrefProvider::PrefProvider", nullptr},
     {"task_scheduler", "*", nullptr},
     {"toplevel", "*", nullptr},
     {TRACE_DISABLED_BY_DEFAULT("cpu_profiler"), "*", nullptr},

components/content_settings/core/browser/content_settings_pref_provider.cc

@@ -15,6 +15,7 @@
 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/time/default_clock.h"
+#include "base/trace_event/trace_event.h"
 #include "components/content_settings/core/browser/content_settings_info.h"
 #include "components/content_settings/core/browser/content_settings_pref.h"
 #include "components/content_settings/core/browser/content_settings_registry.h"
@@ -93,6 +94,7 @@ PrefProvider::PrefProvider(PrefService* prefs,
       is_incognito_(incognito),
       store_last_modified_(store_last_modified),
       clock_(base::DefaultClock::GetInstance()) {
+  TRACE_EVENT_BEGIN0("startup", "PrefProvider::PrefProvider");
   DCHECK(prefs_);
   // Verify preferences version.
   if (!prefs_->HasPrefPath(prefs::kContentSettingsVersion)) {
@@ -101,6 +103,7 @@ PrefProvider::PrefProvider(PrefService* prefs,
   }
   if (prefs_->GetInteger(prefs::kContentSettingsVersion) >
       ContentSettingsPattern::kContentSettingsPatternVersion) {
+    TRACE_EVENT_END0("startup", "PrefProvider::PrefProvider");
     return;
   }
 
@@ -135,14 +138,17 @@ PrefProvider::PrefProvider(PrefService* prefs,
     }
   }
 
+  size_t num_exceptions = 0;
   if (!is_incognito_) {
-    size_t num_exceptions = 0;
     for (const auto& pref : content_settings_prefs_)
       num_exceptions += pref.second->GetNumExceptions();
 
     UMA_HISTOGRAM_COUNTS_1M("ContentSettings.NumberOfExceptions",
                             num_exceptions);
   }
+
+  TRACE_EVENT_END1("startup", "PrefProvider::PrefProvider",
+                   "NumberOfExceptions", num_exceptions);
 }
 
 PrefProvider::~PrefProvider() {