Add policy provider that would filter extensions/apps allowed on the

chrome/browser/chromeos/extensions/signin_screen_policy_provider.h

Index: chrome/browser/chromeos/extensions/signin_screen_policy_provider.h
diff --git a/chrome/browser/chromeos/extensions/signin_screen_policy_provider.h b/chrome/browser/chromeos/extensions/signin_screen_policy_provider.h
new file mode 100644
index 0000000000000000000000000000000000000000..9e2785a1afd13801bbc3ff74b90e927dce12855d
--- /dev/null
+++ b/chrome/browser/chromeos/extensions/signin_screen_policy_provider.h
@@ -0,0 +1,40 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_CHROMEOS_EXTENSIONS_SIGNIN_SCREEN_POLICY_PROVIDER_H_
+#define CHROME_BROWSER_CHROMEOS_EXTENSIONS_SIGNIN_SCREEN_POLICY_PROVIDER_H_
+
+#include <string>
+
+#include "base/auto_reset.h"
+#include "base/macros.h"
+#include "base/strings/string16.h"
+#include "extensions/browser/management_policy.h"
+#include "extensions/common/extension.h"
+
+namespace chromeos {
+
+// A managed policy that guards which extensions can be loaded on
+// sign-in screen.
+class SigninScreenPolicyProvider
+    : public extensions::ManagementPolicy::Provider {
+ public:
+  SigninScreenPolicyProvider();
+  ~SigninScreenPolicyProvider() override;
+
+  // extensions::ManagementPolicy::Provider:
+  std::string GetDebugPolicyProviderName() const override;
+  bool UserMayLoad(const extensions::Extension* extension,
+                   base::string16* error) const override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SigninScreenPolicyProvider);
+};
+
+std::unique_ptr<base::AutoReset<bool>>
+GetScopedSigninScreenPolicyProviderDisablerForTesting();
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_EXTENSIONS_SIGNIN_SCREEN_POLICY_PROVIDER_H_