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

chrome/browser/ui/webui/ntp/most_visited_handler.cc

Index: chrome/browser/ui/webui/ntp/most_visited_handler.cc
diff --git a/chrome/browser/ui/webui/ntp/most_visited_handler.cc b/chrome/browser/ui/webui/ntp/most_visited_handler.cc
index 39a1f2fb5c85c239559cf13fcd4d04a4700fe738..fe4c7a3a36e13e92d48758f3e45b41b3becd0a36 100644
--- a/chrome/browser/ui/webui/ntp/most_visited_handler.cc
+++ b/chrome/browser/ui/webui/ntp/most_visited_handler.cc
@@ -20,6 +20,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread.h"
 #include "base/values.h"
+#include "chrome/browser/favicon/fallback_icon_service_factory.h"
 #include "chrome/browser/history/top_sites_factory.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/thumbnails/thumbnail_list_source.h"
@@ -36,6 +37,7 @@
 #include "chrome/common/url_constants.h"
 #include "components/history/core/browser/page_usage_data.h"
 #include "components/history/core/browser/top_sites.h"
+#include "components/keyed_service/core/service_access_type.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "content/public/browser/navigation_controller.h"
 #include "content/public/browser/navigation_entry.h"
@@ -81,7 +83,10 @@ void MostVisitedHandler::RegisterMessages() {
   content::URLDataSource::Add(profile, new ThumbnailListSource(profile));
 
   // Register chrome://fallback-icon as a data source for fallback icons.
-  content::URLDataSource::Add(profile, new FallbackIconSource());
+  content::URLDataSource::Add(profile,
+      new FallbackIconSource(
+          FallbackIconServiceFactory::GetForProfile(
+              profile, ServiceAccessType::EXPLICIT_ACCESS)));
 
   // Register chrome://favicon as a data source for favicons.
   content::URLDataSource::Add(