Split WarningService from ExtensionSystem.

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 283bf6d069dec3ceba3cb2021f9fc286c709d82e..5aa9a50a885898da5650caa9bafb849e9f42ba5d 100644
--- a/extensions/browser/warning_service.h
+++ b/extensions/browser/warning_service.h
@@ -12,6 +12,7 @@
 #include "base/observer_list.h"
 #include "base/scoped_observer.h"
 #include "base/threading/non_thread_safe.h"
+#include "components/keyed_service/core/keyed_service.h"
 #include "extensions/browser/extension_registry_observer.h"
 #include "extensions/browser/warning_set.h"
 
@@ -31,7 +32,8 @@ 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.
-class WarningService : public ExtensionRegistryObserver,
+class WarningService : public KeyedService,
+                       public ExtensionRegistryObserver,
                        public base::NonThreadSafe {
  public:
   class Observer {
@@ -44,6 +46,10 @@ class WarningService : public ExtensionRegistryObserver,
   explicit WarningService(content::BrowserContext* browser_context);
   ~WarningService() override;
 
+  // Get the instance of the WarningService for |browser_context|.
+  // Redirected in incognito.
+  static WarningService* Get(content::BrowserContext* browser_context);
+
   // Clears all warnings of types contained in |types| and notifies observers
   // of the changed warnings.
   void ClearWarnings(const std::set<Warning::WarningType>& types);