Always use ENABLE_PLUGINS to indicate plugins support.

build/config/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/allocator.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
@@ skipping 50 matching lines @@
     # TODO(brettw) should probably be "=1"
     defines += [ "ENABLE_PEPPER_CDMS" ]
   }
   if (enable_browser_cdms) {
     # TODO(brettw) should probably be "=1"
     defines += [ "ENABLE_BROWSER_CDMS" ]
   }
   if (enable_plugins) {
     defines += [ "ENABLE_PLUGINS=1" ]
   }
+  if (enable_pdf) {
+    defines += [ "ENABLE_PDF=1" ]
+  }
   if (enable_basic_printing || enable_print_preview) {
     # Convenience define for ENABLE_BASIC_PRINTING || ENABLE_PRINT_PREVIEW.
     defines += [ "ENABLE_PRINTING=1" ]
     if (enable_basic_printing) {
       # Enable basic printing support and UI.
       defines += [ "ENABLE_BASIC_PRINTING=1" ]
     }
     if (enable_print_preview) {
       # Enable printing with print preview.
       # Can be defined without ENABLE_BASIC_PRINTING.
@@ skipping 360 matching lines @@
     # with precompiled headers since the source file that's "compiled" for
     # making the precompiled header is empty.
     #
     # This error doesn't happen every time. In VS2013, it seems if the .pch
     # file doesn't exist, no error will be generated (probably MS tested this
     # case but forgot the other one?). To reproduce this error, do a build,
     # then delete the precompile.c.obj file, then build again.
     cflags_c = [ "/wd4206" ]
   }
 }