Convert enable_plugins to a buildflag header.

content/test/BUILD.gn

 # Copyright 2014 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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
+import("//ppapi/features/features.gni")
 import("//testing/test.gni")
 import("//third_party/WebKit/public/public_features.gni")
 import("//v8/gni/v8.gni")
 
 # Use a static library here because many test binaries depend on this but don't
 # require many files from it. This makes linking more efficient.
 static_library("test_support") {
   testonly = true
 
   # See comment at the top of //content/BUILD.gn for why this is disabled in
@@ skipping 673 matching lines @@
     "//ipc:test_support",
     "//media",
     "//media:test_support",
     "//media/audio:test_support",
     "//media/base:test_support",
     "//mojo/edk/system",
     "//mojo/edk/test:test_support",
     "//mojo/public/cpp/bindings",
     "//mojo/public/js",
     "//net:test_support",
+    "//ppapi/features",
     "//services/service_manager/public/cpp",
     "//storage/browser",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/WebKit/public:blink",
     "//third_party/leveldatabase",
     "//third_party/mesa:osmesa",
     "//third_party/zlib",
     "//ui/accessibility",
     "//ui/accessibility:ax_gen",
@@ skipping 690 matching lines @@
     "//media/base:test_support",
     "//media/blink",
     "//media/capture",
     "//media/midi:midi",
     "//media/midi:mojo_cpp_sources",
     "//mojo/edk/test:test_support",
     "//mojo/public/cpp/bindings",
     "//net:extras",
     "//net:test_support",
     "//ppapi/c",
+    "//ppapi/features",
     "//printing",
     "//skia",
     "//sql",
     "//sql:test_support",
     "//storage/browser",
     "//storage/common",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/WebKit/public:blink",
     "//third_party/icu",
@@ skipping 285 matching lines @@
   if (is_android) {
     deps += [ "//testing/android/native_test:native_test_native_code" ]
   }
 }
 
 group("fuzzers") {
   deps = [
     "//content/test/fuzzer",
   ]
 }