Extract InstallVerifier from ExtensionSystem.

extensions/browser/extension_system.h

Index: extensions/browser/extension_system.h
diff --git a/extensions/browser/extension_system.h b/extensions/browser/extension_system.h
index e5dd4680033c715d0feeb1f01c861fe38908d2bf..71ed7b697efffbefc83b8cdbe8f2543d227636ee 100644
--- a/extensions/browser/extension_system.h
+++ b/extensions/browser/extension_system.h
@@ -35,7 +35,6 @@ class EventRouter;
 class Extension;
 class ExtensionSet;
 class InfoMap;
-class InstallVerifier;
 class LazyBackgroundTaskQueue;
 class ManagementPolicy;
 class OneShotEvent;
@@ -94,9 +93,6 @@ class ExtensionSystem : public KeyedService {
   // The EventRouter is created at startup.
   virtual EventRouter* event_router() = 0;
 
-  // The InstallVerifier is created at startup.
-  virtual InstallVerifier* install_verifier() = 0;
-
   // Returns the QuotaService that limits calls to certain extension functions.
   // Lives on the UI thread. Created at startup.
   virtual QuotaService* quota_service() = 0;