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

chrome/browser/chromeos/extensions/signin_screen_policy_provider.cc

+// 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.
+
+#include "chrome/browser/chromeos/extensions/signin_screen_policy_provider.h"
+
+#include <stddef.h>
+
+#include <cstddef>
+#include <string>
+
+#include "base/logging.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/values.h"
+#include "chrome/grit/generated_resources.h"
+#include "extensions/common/extension.h"
+#include "extensions/common/features/behavior_feature.h"
+#include "extensions/common/features/feature.h"
+#include "extensions/common/features/feature_provider.h"
+#include "extensions/common/manifest.h"
+#include "extensions/common/manifest_constants.h"
+#include "ui/base/l10n/l10n_util.h"
+
+namespace chromeos {
+
+SigninScreenPolicyProvider::SigninScreenPolicyProvider() {}
+
+SigninScreenPolicyProvider::~SigninScreenPolicyProvider() {}
+
+std::string SigninScreenPolicyProvider::GetDebugPolicyProviderName() const {
+#if defined(NDEBUG)
+  NOTREACHED();
+  return std::string();
+#else
+  return "Guard for sign-in screen";
+#endif
+}
+
+bool SigninScreenPolicyProvider::UserMayLoad(
+    const extensions::Extension* extension,
+    base::string16* error) const {
+  const extensions::Feature* feature =
+      extensions::FeatureProvider::GetBehaviorFeature(
+          extensions::BehaviorFeature::kSigninScreen);
+
+  if (feature) {
+    extensions::Feature::Availability availability =
+        feature->IsAvailableToExtension(extension);
+
+    if (availability.is_available()) {
+      VLOG(0) << "Extension allowed : " << extension->id() << " / "
+              << extension->name();
+      return true;
+    }
+    VLOG(0) << "Extension disabled : " << extension->id() << " / "
+            << extension->name() << " because of " << availability.message();
+  } else {
+    VLOG(0) << "Feature " << extensions::BehaviorFeature::kSigninScreen
+            << " is not defined";
+  }
+
+  // Disallow all other extensions.
+  if (error) {
+    *error =
+        l10n_util::GetStringFUTF16(IDS_EXTENSION_CANT_INSTALL_ON_LOGIN_SCREEN,
+                                   base::UTF8ToUTF16(extension->name()),
+                                   base::UTF8ToUTF16(extension->id()));
+  }
+  return false;
+}
+
+}  // namespace chromeos