Regularize ownerships and lifecycle for storage monitor platform classes.

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

Index: chrome/browser/chromeos/chrome_browser_main_chromeos.cc
diff --git a/chrome/browser/chromeos/chrome_browser_main_chromeos.cc b/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
index b11f3ad98334e597208fb1c7b7b3cf61d0c14b20..a3d5e629c4fcbf2205b62afd98379a2e3ebb7b9f 100644
--- a/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
+++ b/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
@@ -544,6 +544,8 @@ void ChromeBrowserMainPartsChromeos::PreProfileInit() {
                                   &tracker_);
 #endif
 
+  storage_monitor_ = new StorageMonitorCros();
+
   // In Aura builds this will initialize ash::Shell.
   ChromeBrowserMainPartsLinux::PreProfileInit();
 }
@@ -619,7 +621,7 @@ void ChromeBrowserMainPartsChromeos::PostProfileInit() {
   }
   chromeos::accessibility::Initialize();
 
-  storage_monitor_ = new StorageMonitorCros();
+  storage_monitor_->Init();
 
   // Initialize the network portal detector for Chrome OS. The network
   // portal detector starts to listen for notifications from