Move enable_pdf to a buildflag header.

chrome/app/chrome_main_delegate.cc

Index: chrome/app/chrome_main_delegate.cc
diff --git a/chrome/app/chrome_main_delegate.cc b/chrome/app/chrome_main_delegate.cc
index da9719236a12d569031073799a30cf0a5640faa1..2d2b8c7c48a79ccac6a05daaecb6cd7b4bb68d35 100644
--- a/chrome/app/chrome_main_delegate.cc
+++ b/chrome/app/chrome_main_delegate.cc
@@ -51,6 +51,7 @@
 #include "content/public/common/content_paths.h"
 #include "content/public/common/content_switches.h"
 #include "extensions/common/constants.h"
+#include "pdf/features.h"
 #include "ppapi/features/features.h"
 #include "printing/features/features.h"
 #include "ui/base/material_design/material_design_controller.h"
@@ -925,7 +926,7 @@ void ChromeMainDelegate::SandboxInitialized(const std::string& process_type) {
       nacl_plugin::PPP_InitializeModule,
       nacl_plugin::PPP_ShutdownModule);
 #endif
-#if BUILDFLAG(ENABLE_PLUGINS) && defined(ENABLE_PDF)
+#if BUILDFLAG(ENABLE_PLUGINS) && BUILDFLAG(ENABLE_PDF)
   ChromeContentClient::SetPDFEntryFunctions(
       chrome_pdf::PPP_GetInterface,
       chrome_pdf::PPP_InitializeModule,