Replace deprecated base::NonThreadSafe in extensions in favor of SequenceChecker.

extensions/browser/warning_service.h

Index: extensions/browser/warning_service.h
diff --git a/extensions/browser/warning_service.h b/extensions/browser/warning_service.h
index 8fd3b633d0609cc3cbe63c57a66e936ed328d46d..807af1cf7ffb022dc692ab0eeb099067d8a71794 100644
--- a/extensions/browser/warning_service.h
+++ b/extensions/browser/warning_service.h
@@ -11,7 +11,7 @@
 
 #include "base/observer_list.h"
 #include "base/scoped_observer.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "extensions/browser/extension_registry_observer.h"
 #include "extensions/browser/warning_set.h"
@@ -30,9 +30,7 @@ class ExtensionRegistry;
 // conflicting modifications of network requests by extensions, slow extensions,
 // etc.) trigger a warning badge in the UI and and provide means to resolve
 // them. This class must be used on the UI thread only.

[Devlin, 2017/05/30 19:06:47]

I'm not sure that SequenceChecker is right for this class (and not sure that
base::NonThreadSafe was entirely right, either).  This is designed to be used
specifically on the UI thread *only*, and uses UI-thread concepts
(BrowserContext and related).  I think what we want instead is to replace
CalledOnValidThread() or CALLED_ON_VALID_SEQUENCE with
DCHECK_CURRENTLY_ON(content::BrowserThread::UI) or ThreadChecker.

[gab, 2017/05/31 17:52:28]

Done.

-class WarningService : public KeyedService,
-                       public ExtensionRegistryObserver,
-                       public base::NonThreadSafe {
+class WarningService : public KeyedService, public ExtensionRegistryObserver {
  public:
   class Observer {
    public:
@@ -91,6 +89,8 @@ class WarningService : public KeyedService,
       extension_registry_observer_;
 
   base::ObserverList<Observer> observer_list_;
+
+  SEQUENCE_CHECKER(sequence_checker_);
 };
 
 }  // namespace extensions