[NTP] Change the include condition on local_files_ntp_source to be !is_chrome_branded

BUG=515743
TBR=thestig

Review URL: https://codereview.chromium.org/1389073002

Cr-Commit-Position: refs/heads/master@{#352694}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 348198d..867e6d8d 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -683,7 +683,7 @@
     ]
   }
 
-  if (!is_official_build) {
+  if (!is_chrome_branded) {
     sources += [
       "search/local_files_ntp_source.cc",
       "search/local_files_ntp_source.h",