Conditionally convert V8 build overrides to declare_args.

build_overrides/v8.gni

 # Copyright 2015 The V8 project 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/v8_target_cpu.gni")
+# This file should be empty.
 
-if (((v8_current_cpu == "x86" || v8_current_cpu == "x64" ||
-      v8_current_cpu == "x87") && (is_linux || is_mac)) ||
-    (v8_current_cpu == "ppc64" && is_linux)) {
-  v8_enable_gdbjit_default = true
-}
-
-v8_imminent_deprecation_warnings_default = true
-
-# Add simple extras solely for the purpose of the cctests.
-v8_extra_library_files = [ "//test/cctest/test-extra.js" ]
-v8_experimental_extra_library_files =
-    [ "//test/cctest/test-experimental-extra.js" ]
-
-v8_enable_inspector_override = true
-
-declare_args() {
-  # Use static libraries instead of source_sets.
-  v8_static_library = false
-}
+# TODO(brettw) http://crbug.com/684096 Remove this when all callers are updated
+# to use the new build overrides system.