Convert enable_plugins to a buildflag header.

chrome/browser/download/download_target_determiner.h

Index: chrome/browser/download/download_target_determiner.h
diff --git a/chrome/browser/download/download_target_determiner.h b/chrome/browser/download/download_target_determiner.h
index f96e79cf9549c3474d072c8f2b13dc37664627fb..19c865854f11ebf21eb86272bb0c448c6fc133be 100644
--- a/chrome/browser/download/download_target_determiner.h
+++ b/chrome/browser/download/download_target_determiner.h
@@ -20,6 +20,7 @@
 #include "content/public/browser/download_danger_type.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_manager_delegate.h"
+#include "ppapi/features/features.h"
 
 class ChromeDownloadManagerDelegate;
 class Profile;
@@ -220,7 +221,7 @@ class DownloadTargetDeterminer
   // - STATE_DETERMINE_IF_ADOBE_READER_UP_TO_DATE.
   Result DoDetermineIfHandledSafely();
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
   // Callback invoked when a decision is available about whether the file type
   // can be handled safely by the browser.
   void DetermineIfHandledSafelyDone(bool is_handled_safely);