UMA: prefer nullptr to NULL

No change to logic. This updates C++ code in the metrics component to
use nullptr instead of NULL. This is to align with the chromium C++
styleguide.

Bug: 1010369
Test: git cl presubmit --upload
Change-Id: Ib4133584972ae6069e469c58798cd1a323b4eeec
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1835091Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Nate Fischer <ntfschr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#702718}

components/metrics/metrics_log_manager.h

@@ -33,13 +33,13 @@ class MetricsLogManager {
   MetricsLog* current_log() { return current_log_.get(); }
 
   // Closes |current_log_|, compresses it, and stores it in the |log_store| for
-  // later, leaving |current_log_| NULL.
+  // later, leaving |current_log_| nullptr.
   void FinishCurrentLog(MetricsLogStore* log_store);
 
   // Closes and discards |current_log|.
   void DiscardCurrentLog();
 
-  // Sets current_log to NULL, but saves the current log for future use with
+  // Sets current_log to nullptr, but saves the current log for future use with
   // ResumePausedLog(). Only one log may be paused at a time.
   // TODO(stuartmorgan): Pause/resume support is really a workaround for a
   // design issue in initial log writing; that should be fixed, and pause/resume

components/metrics/metrics_state_manager.h

@@ -91,9 +91,9 @@ class MetricsStateManager final {
   CreateLowEntropyProvider();
 
   // Creates the MetricsStateManager, enforcing that only a single instance
-  // of the class exists at a time. Returns NULL if an instance exists already.
-  // On Windows, |backup_registry_key| is used to store a backup of the clean
-  // exit beacon. It is ignored on other platforms.
+  // of the class exists at a time. Returns nullptr if an instance exists
+  // already. On Windows, |backup_registry_key| is used to store a backup of the
+  // clean exit beacon. It is ignored on other platforms.
   static std::unique_ptr<MetricsStateManager> Create(
       PrefService* local_state,
       EnabledStateProvider* enabled_state_provider,

components/metrics/net/wifi_access_point_info_provider_chromeos.cc

@@ -101,7 +101,7 @@ void WifiAccessPointInfoProviderChromeos::ParseInfo(
 
   properties.GetStringWithoutPathExpansion(
       shill::kWifiBSsid, &wifi_access_point_info_.bssid);
-  const base::DictionaryValue* vendor_dict = NULL;
+  const base::DictionaryValue* vendor_dict = nullptr;
   if (!properties.GetDictionaryWithoutPathExpansion(
           shill::kWifiVendorInformationProperty,
           &vendor_dict))

components/metrics/serialization/serialization_utils.h

@@ -19,7 +19,7 @@ namespace SerializationUtils {
 
 // Deserializes a sample passed as a string and return a sample.
 // The return value will either be a scoped_ptr to a Metric sample (if the
-// deserialization was successful) or a NULL scoped_ptr.
+// deserialization was successful) or a nullptr scoped_ptr.
 std::unique_ptr<MetricSample> ParseSample(const std::string& sample);
 
 // Reads all samples from a file and truncate the file when done.

components/metrics/system_session_analyzer_win.cc

@@ -134,7 +134,7 @@ bool SystemSessionAnalyzer::FetchEvents(size_t requested_events,
 
   // Retrieve events: 2 events per session, plus the current session's start.
   DWORD desired_event_cnt = requested_events;
-  std::vector<EVT_HANDLE> events_raw(desired_event_cnt, NULL);
+  std::vector<EVT_HANDLE> events_raw(desired_event_cnt, nullptr);
   DWORD event_cnt = 0U;
   BOOL success = ::EvtNext(query_handle_.get(), desired_event_cnt,
                            events_raw.data(), kTimeoutMs, 0, &event_cnt);