Convert enable_plugins to a buildflag header.

content/zygote/zygote_main_linux.cc

Index: content/zygote/zygote_main_linux.cc
diff --git a/content/zygote/zygote_main_linux.cc b/content/zygote/zygote_main_linux.cc
index 40260cd208bd2c86f14451fbbb9681f67065732d..945cf6931bb3cde3130f7897d78409ef2ae79968 100644
--- a/content/zygote/zygote_main_linux.cc
+++ b/content/zygote/zygote_main_linux.cc
@@ -44,6 +44,7 @@
 #include "content/public/common/sandbox_linux.h"
 #include "content/public/common/zygote_fork_delegate_linux.h"
 #include "content/zygote/zygote_linux.h"
+#include "ppapi/features/features.h"
 #include "sandbox/linux/services/credentials.h"
 #include "sandbox/linux/services/init_process_reaper.h"
 #include "sandbox/linux/services/namespace_sandbox.h"
@@ -60,7 +61,7 @@
 #include <sys/prctl.h>
 #endif
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 #include "content/common/pepper_plugin_list.h"
 #include "content/public/common/pepper_plugin_info.h"
 #endif
@@ -311,7 +312,7 @@ struct tm* localtime64_r_override(const time_t* timep, struct tm* result) {
   return res;
 }
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
 // Loads the (native) libraries but does not initialize them (i.e., does not
 // call PPP_InitializeModule). This is needed by the zygote on Linux to get
 // access to the plugins before entering the sandbox.
@@ -357,7 +358,7 @@ static void ZygotePreSandboxInit() {
   // will work inside the sandbox.
   RAND_set_urandom_fd(base::GetUrandomFD());
 
-#if defined(ENABLE_PLUGINS)
+#if BUILDFLAG(ENABLE_PLUGINS)
   // Ensure access to the Pepper plugins before the sandbox is turned on.
   PreloadPepperPlugins();
 #endif