Convert enable_plugins to a buildflag header.

content/browser/download/download_browsertest.cc

Index: content/browser/download/download_browsertest.cc
diff --git a/content/browser/download/download_browsertest.cc b/content/browser/download/download_browsertest.cc
index a7260a3939dabcd48b76eff8f94221954a888e67..fd3e8ba96f181a36b6030cfcde8750c6869a0500 100644
--- a/content/browser/download/download_browsertest.cc
+++ b/content/browser/download/download_browsertest.cc
@@ -55,11 +55,12 @@
 #include "net/test/embedded_test_server/http_response.h"
 #include "net/test/url_request/url_request_mock_http_job.h"
 #include "net/test/url_request/url_request_slow_download_job.h"
+#include "ppapi/features/features.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "url/gurl.h"
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 #include "content/browser/plugin_service_impl.h"
 #endif
 
@@ -804,7 +805,7 @@ IN_PROC_BROWSER_TEST_F(DownloadContentTest, MultiDownload) {
       file2, GetTestFilePath("download", "download-test.lib")));
 }
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 // Content served with a MIME type of application/octet-stream should be
 // downloaded even when a plugin can be found that handles the file type.
 IN_PROC_BROWSER_TEST_F(DownloadContentTest, DownloadOctetStream) {