Move SetupMetrics() to PreMainMessageLoopRun

ios/chrome/browser/ios_chrome_main_parts.mm

Index: ios/chrome/browser/ios_chrome_main_parts.mm
diff --git a/ios/chrome/browser/ios_chrome_main_parts.mm b/ios/chrome/browser/ios_chrome_main_parts.mm
index 722cad2bed9daa63425805ca552ac0badeaa4cec..e295f9fa993fc7daba857985cef140772b162181 100644
--- a/ios/chrome/browser/ios_chrome_main_parts.mm
+++ b/ios/chrome/browser/ios_chrome_main_parts.mm
@@ -132,8 +132,6 @@ void IOSChromeMainParts::PreCreateThreads() {
 
   // Task Scheduler initialization needs to be here for the following reasons:
   //   * After |SetupFieldTrials()|: Initialization uses variations.
-  //   * Before |SetupMetrics()|: |SetupMetrics()| uses the blocking pool. The
-  //         Task Scheduler must do any necessary redirection before then.
   //   * Near the end of |PreCreateThreads()|: The TaskScheduler needs to be
   //         created before any other threads are (by contract) but it creates
   //         threads itself so instantiating it earlier is also incorrect.
@@ -141,7 +139,6 @@ void IOSChromeMainParts::PreCreateThreads() {
   // shutdown call may also need to be moved.
   task_scheduler_util::InitializeDefaultBrowserTaskScheduler();
 
-  SetupMetrics();
 
   // Initialize FieldTrialSynchronizer system.
   field_trial_synchronizer_.reset(new ios::FieldTrialSynchronizer);
@@ -150,6 +147,10 @@ void IOSChromeMainParts::PreCreateThreads() {
 }
 
 void IOSChromeMainParts::PreMainMessageLoopRun() {
+  // This must occur at PreMainMessageLoopRun because |SetupMetrics()| uses the
+  // blocking pool, which is disabled until the CreateThreads phase of startup.
+  SetupMetrics();
+
   // Now that the file thread has been started, start recording.
   StartMetricsRecording();