Implement CurrentProcessInfo::CreationTime() for Linux.

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index bc285f01bd9b70e34ca10886ae57dd784b2dc5d1..bb7a7fa91749fa5a96159b208151bf6e9b3a24a4 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -689,9 +689,6 @@ void ChromeBrowserMainParts::RecordBrowserStartupTime() {
 
   bool is_first_run = first_run::IsChromeFirstRun();
 
-// CurrentProcessInfo::CreationTime() is currently only implemented on Mac and
-// Windows.
-#if defined(OS_MACOSX) || defined(OS_WIN)
   const base::Time* process_creation_time =
       base::CurrentProcessInfo::CreationTime();
 
@@ -699,7 +696,6 @@ void ChromeBrowserMainParts::RecordBrowserStartupTime() {
     RecordPreReadExperimentTime("Startup.BrowserMessageLoopStartTime",
         base::Time::Now() - *process_creation_time);
   }
-#endif  // defined(OS_MACOSX) || defined(OS_WIN)
 
   // Record collected startup metrics.
   startup_metric_utils::OnBrowserStartupComplete(is_first_run);