Add new histograms to measure time in PreMainMessageLoop.

chrome/browser/browser_process_impl.cc

Index: chrome/browser/browser_process_impl.cc
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index 52bab4a24adfc497dae16bee50d4f1bb03609300..ec6628e1d27ba98c47dec9b3badff08ce98ccfc2 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -16,6 +16,7 @@
 #include "base/debug/leak_annotations.h"
 #include "base/files/file_path.h"
 #include "base/metrics/field_trial.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
 #include "base/prefs/json_pref_store.h"
 #include "base/prefs/pref_registry_simple.h"
@@ -24,6 +25,7 @@
 #include "base/threading/thread.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/time/default_tick_clock.h"
+#include "base/trace_event/trace_event.h"
 #include "chrome/browser/chrome_browser_main.h"
 #include "chrome/browser/chrome_content_browser_client.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ -996,6 +998,10 @@ void BrowserProcessImpl::PreCreateThreads() {
 }
 
 void BrowserProcessImpl::PreMainMessageLoopRun() {
+  TRACE_EVENT0("startup", "BrowserProcessImpl::PreMainMessageLoopRun");
+  SCOPED_UMA_HISTOGRAM_TIMER(
+      "Startup.BrowserProcessImplPreMainMessageLoopRunTime");

[Alexei Svitkine (slow), 2015/02/13 18:01:30]

Nit: To make these a bit more readable, how about adding an underscore between
the class and method name - i.e:

Startup.BrowserProcessImpl_PreMainMessageLoopRunTime

[rkaplow, 2015/02/13 18:44:23]

Done.

+
 #if defined(ENABLE_CONFIGURATION_POLICY)
   // browser_policy_connector() is created very early because local_state()
   // needs policy to be initialized with the managed preference values.