Convert enable_plugins to a buildflag header.

chrome/browser/permissions/permission_manager.cc

Index: chrome/browser/permissions/permission_manager.cc
diff --git a/chrome/browser/permissions/permission_manager.cc b/chrome/browser/permissions/permission_manager.cc
index 9b54d1561e26c849784bc26e3e3bdc83f83db3b5..031d46958541a6651e6c8ce78fe8ba39fa268f72 100644
--- a/chrome/browser/permissions/permission_manager.cc
+++ b/chrome/browser/permissions/permission_manager.cc
@@ -30,8 +30,9 @@
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/web_contents.h"
+#include "ppapi/features/features.h"
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 #include "chrome/browser/plugins/flash_permission_context.h"
 #endif
 
@@ -257,7 +258,7 @@ PermissionManager::PermissionManager(Profile* profile)
           CONTENT_SETTINGS_TYPE_MEDIASTREAM_CAMERA);
   permission_contexts_[PermissionType::BACKGROUND_SYNC] =
       base::MakeUnique<BackgroundSyncPermissionContext>(profile);
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
   permission_contexts_[PermissionType::FLASH] =
       base::MakeUnique<FlashPermissionContext>(profile);
 #endif