[signin] Add DICe flow for account consistency requests.

components/signin/core/browser/dice_header_helper.h

+// Copyright 2017 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 COMPONENTS_SIGNIN_CORE_BROWSER_DICE_HEADER_HELPER_H_
+#define COMPONENTS_SIGNIN_CORE_BROWSER_DICE_HEADER_HELPER_H_
+
+#include <string>
+
+#include "components/signin/core/browser/signin_header_helper.h"
+
+class GURL;
+
+namespace signin {
+
+extern const char kDiceRequestHeader[];
+
+// SigninHeaderHelper implementation managing the Dice header.
+class DiceHeaderHelper : public SigninHeaderHelper {
+ private:
+  // SigninHeaderHelper implementation:
+  bool IsUrlEligibleForRequestHeader(const GURL& url) override;
+  std::string BuildRequestHeader(bool is_header_request,
+                                 const GURL& url,
+                                 const std::string& account_id,
+                                 int profile_mode_mask) override;
+};
+
+}  // namespace signin
+
+#endif  // COMPONENTS_SIGNIN_CORE_BROWSER_DICE_HEADER_HELPER_H_