Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

chrome/browser/extensions/api/storage/storage_api.h

Index: chrome/browser/extensions/api/storage/storage_api.h
diff --git a/chrome/browser/extensions/api/storage/storage_api.h b/chrome/browser/extensions/api/storage/storage_api.h
index eb9411f1ed4b7bf42aa5bc15e8db99b9d200add9..d6d38f6d0ffbe293605deaa2486e24a84fa2b0f5 100644
--- a/chrome/browser/extensions/api/storage/storage_api.h
+++ b/chrome/browser/extensions/api/storage/storage_api.h
@@ -7,10 +7,10 @@
 
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
-#include "chrome/browser/extensions/api/storage/settings_namespace.h"
 #include "chrome/browser/extensions/api/storage/settings_observer.h"
 #include "chrome/browser/extensions/chrome_extension_function.h"
 #include "chrome/browser/value_store/value_store.h"
+#include "extensions/browser/api/storage/settings_namespace.h"
 
 namespace extensions {