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

chrome/browser/search/instant_service.cc

Index: chrome/browser/search/instant_service.cc
diff --git a/chrome/browser/search/instant_service.cc b/chrome/browser/search/instant_service.cc
index e785e0c04a061e5c565cc9d9f2119ad21c4a0399..b35fb4c9ef0fb6e05cf1f7ea95104ca6f275389a 100644
--- a/chrome/browser/search/instant_service.cc
+++ b/chrome/browser/search/instant_service.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/search/instant_service.h"
 
 #include "chrome/browser/chrome_notification_types.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/search/instant_io_context.h"
@@ -25,6 +26,7 @@
 #include "chrome/browser/ui/webui/theme_source.h"
 #include "chrome/common/render_messages.h"
 #include "components/history/core/browser/top_sites.h"
+#include "components/keyed_service/core/service_access_type.h"
 #include "components/search_engines/template_url_service.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
@@ -125,7 +127,10 @@ InstantService::InstantService(Profile* profile)
   content::URLDataSource::Add(profile_, new ThumbnailListSource(profile_));
 #endif  // !defined(OS_ANDROID)
 
-  content::URLDataSource::Add(profile_, new FallbackIconSource());
+  content::URLDataSource::Add(profile_,
+      new FallbackIconSource(
+          FallbackIconServiceFactory::GetForProfile(
+              profile_, ServiceAccessType::EXPLICIT_ACCESS)));
   content::URLDataSource::Add(
       profile_, new FaviconSource(profile_, FaviconSource::FAVICON));
   content::URLDataSource::Add(profile_, new MostVisitedIframeSource());