Move enable_webrtc 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("//media/media_options.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
@@ skipping 1693 matching lines @@
   if (is_android) {
     deps += [ "//testing/android/native_test:native_test_native_code" ]
   }
 }
 
 group("fuzzers") {
   deps = [
     "//content/test/fuzzer",
   ]
 }