[Fallback Icons] Refactor FallbackIconService to be a BrowserContext-level singleton

chrome/browser/favicon/chrome_fallback_icon_client.h

+// Copyright 2015 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_FAVICON_CHROME_FALLBACK_ICON_CLIENT_H_
+#define CHROME_BROWSER_FAVICON_CHROME_FALLBACK_ICON_CLIENT_H_
+
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/strings/string16.h"
+#include "components/favicon/core/fallback_icon_client.h"
+
+class GURL;
+
+// ChromeFallbackIconClient implements the FallbackIconClient interface.
+class ChromeFallbackIconClient : public FallbackIconClient {
+ public:
+  ChromeFallbackIconClient();
+  ~ChromeFallbackIconClient() override;
+
+  // FallbackIconClient implementation:
+  const std::vector<std::string>& GetFontNameList() const override;
+
+  base::string16 GetFallbackIconText(const GURL& url) const override;
+
+ private:
+  std::vector<std::string> font_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeFallbackIconClient);
+};
+
+#endif  // CHROME_BROWSER_FAVICON_CHROME_FALLBACK_ICON_CLIENT_H_