Convert enable_plugins to a buildflag header.

chrome/browser/content_settings/content_settings_browsertest.cc

Index: chrome/browser/content_settings/content_settings_browsertest.cc
diff --git a/chrome/browser/content_settings/content_settings_browsertest.cc b/chrome/browser/content_settings/content_settings_browsertest.cc
index 7d7c3b150a70d19eaae38b2dbbf9448ecae91092..667df3dfdf08f7b5da18547942fb49cac0a6b1aa 100644
--- a/chrome/browser/content_settings/content_settings_browsertest.cc
+++ b/chrome/browser/content_settings/content_settings_browsertest.cc
@@ -345,7 +345,7 @@ IN_PROC_BROWSER_TEST_F(ContentSettingsTest, RedirectCrossOrigin) {
       IsContentBlocked(CONTENT_SETTINGS_TYPE_COOKIES));
 }
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 class PepperContentSettingsSpecialCasesTest : public ContentSettingsTest {
  protected:
   void SetUpCommandLine(base::CommandLine* command_line) override {
@@ -547,4 +547,4 @@ IN_PROC_BROWSER_TEST_F(PepperContentSettingsSpecialCasesJavaScriptBlockedTest,
 }
 #endif  // !defined(DISABLE_NACL)
 
-#endif  // defined(ENABLE_PLUGINS)
+#endif  // BUILDFLAG(ENABLE_PLUGINS)