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

chrome/browser/favicon/chrome_fallback_icon_client.cc

+// 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.
+
+#include "chrome/browser/favicon/chrome_fallback_icon_client.h"
+
+#include "base/i18n/case_conversion.h"
+#include "base/strings/utf_string_conversions.h"
+#include "grit/platform_locale_settings.h"
+#include "net/base/registry_controlled_domains/registry_controlled_domain.h"
+#include "ui/base/l10n/l10n_util.h"
+#include "url/gurl.h"
+
+ChromeFallbackIconClient::ChromeFallbackIconClient() {
+#if defined(OS_CHROMEOS)
+  font_list_.push_back("Noto Sans");
+#elif defined(OS_IOS)
+  font_list_.push_back("Helvetica Neue");
+#else
+  font_list_.push_back(l10n_util::GetStringUTF8(IDS_SANS_SERIF_FONT_FAMILY));
+#endif
+}
+
+ChromeFallbackIconClient::~ChromeFallbackIconClient() {
+}
+
+const std::vector<std::string>& ChromeFallbackIconClient::GetFontNameList()
+    const {
+  return font_list_;
+}
+
+// Returns a single character to represent |url|. To do this we take the first
+// letter in a domain's name and make it upper case.
+base::string16 ChromeFallbackIconClient::GetFallbackIconText(const GURL& url)
+    const {
+  // TODO(huangs): Handle non-ASCII ("xn--") domain names.
+  std::string domain = net::registry_controlled_domains::GetDomainAndRegistry(
+      url, net::registry_controlled_domains::INCLUDE_PRIVATE_REGISTRIES);
+  return domain.empty() ? base::string16() :
+      base::i18n::ToUpper(base::ASCIIToUTF16(domain.substr(0, 1)));
+}