Introduce flag to disable static popular sites.

components/ntp_tiles/popular_sites_impl.cc

Index: components/ntp_tiles/popular_sites_impl.cc
diff --git a/components/ntp_tiles/popular_sites_impl.cc b/components/ntp_tiles/popular_sites_impl.cc
index 7777e37dc47718bdca635e405a29690262ee1137..b6e0e32e1fbd0d5650b3196576e15c2659dd0678 100644
--- a/components/ntp_tiles/popular_sites_impl.cc
+++ b/components/ntp_tiles/popular_sites_impl.cc
@@ -153,6 +153,9 @@ std::unique_ptr<base::ListValue> DefaultPopularSites() {
 #if !defined(OS_ANDROID) && !defined(OS_IOS)
   return base::MakeUnique<base::ListValue>();
 #else
+  if (!ShouldUseBakedInSites()) {
+    return base::MakeUnique<base::ListValue>();
+  }
   std::unique_ptr<base::ListValue> sites =
       base::ListValue::From(base::JSONReader::Read(
           ResourceBundle::GetSharedInstance().GetRawDataResource(