Convert enable_plugins to a buildflag header.

content/renderer/renderer_main.cc

Index: content/renderer/renderer_main.cc
diff --git a/content/renderer/renderer_main.cc b/content/renderer/renderer_main.cc
index a3ffb461a52aaa21db2a68a9ed0cd547f4427fab..e356a096a5fea582240f747261681a64560b59e5 100644
--- a/content/renderer/renderer_main.cc
+++ b/content/renderer/renderer_main.cc
@@ -30,6 +30,7 @@
 #include "content/renderer/render_process_impl.h"
 #include "content/renderer/render_thread_impl.h"
 #include "content/renderer/renderer_main_platform_delegate.h"
+#include "ppapi/features/features.h"
 #include "third_party/WebKit/public/platform/scheduler/renderer/renderer_scheduler.h"
 #include "third_party/skia/include/core/SkGraphics.h"
 #include "ui/base/ui_base_switches.h"
@@ -48,7 +49,7 @@
 #include "third_party/WebKit/public/web/WebView.h"
 #endif  // OS_MACOSX
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 #include "content/renderer/pepper/pepper_plugin_registry.h"
 #endif
 
@@ -158,7 +159,7 @@ int RendererMain(const MainFunctionParams& parameters) {
   // PlatformInitialize uses FieldTrials, so this must happen later.
   platform.PlatformInitialize();
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
   // Load pepper plugins before engaging the sandbox.
   PepperPluginRegistry::GetInstance();
 #endif