Use in-class initializers for base::WeakPtrFactory in chrome/.

Generated by: https://chromium-review.googlesource.com/c/chromium/src/+/1689216

Some existing uses of NULL are replaced with nullptr to remove
presubmit errors.

Bug: 981415
Change-Id: I9824a00bd16e27cf2f0e03e6c7127ffc457b56e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697372
Commit-Queue: Jeremy Roman <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#676912}
diff --git a/chrome/browser/push_messaging/push_messaging_notification_manager.h b/chrome/browser/push_messaging/push_messaging_notification_manager.h
index 41bd07a8..3037534 100644
--- a/chrome/browser/push_messaging/push_messaging_notification_manager.h
+++ b/chrome/browser/push_messaging/push_messaging_notification_manager.h
@@ -110,7 +110,7 @@
       nullptr;
 #endif
 
-  base::WeakPtrFactory<PushMessagingNotificationManager> weak_factory_;
+  base::WeakPtrFactory<PushMessagingNotificationManager> weak_factory_{this};
 
   DISALLOW_COPY_AND_ASSIGN(PushMessagingNotificationManager);
 };