Regularize ownerships and lifecycle for storage monitor platform classes.

chrome/browser/storage_monitor/storage_monitor.h

Index: chrome/browser/storage_monitor/storage_monitor.h
diff --git a/chrome/browser/storage_monitor/storage_monitor.h b/chrome/browser/storage_monitor/storage_monitor.h
index 85b1f1be9cc01acc60e0791193180b85c88d8c2f..35247fbdbf39f8ec3f402ef6143670a25f754043 100644
--- a/chrome/browser/storage_monitor/storage_monitor.h
+++ b/chrome/browser/storage_monitor/storage_monitor.h
@@ -25,6 +25,11 @@ class TransientDeviceIds;
 
 // Base class for platform-specific instances watching for removable storage
 // attachments/detachments.
+// Lifecycle contracts: This class is created by ChromeBrowserMain
+// implementations before the profile is initialized, so listeners can be
+// created during profile construction. The platform-specific initialization,
+// which can lead to calling registered listeners with notifications of
+// attached volumes, will happen after profile construction.
 class StorageMonitor {
  public:
   // This interface is provided to generators of storage notifications.